The Fundamental Understanding of Lithium Polysulfides in Ether-Based Electrolyte for Lithium–Sulfur Batteries

The liquid electrolyte in a lithium–sulfur battery is important for the dissolution–deposition reaction through the solubility of polysulfides. To get insight into the sulfur chemistry, fundamental understanding of the dissolved polysulfides should be explored. In this work, the dissolved forms of Li2S6, as prototypical polysulfides, in 1,2-dimethoxyethane (DME) were studied by ab initio calculations. The calculated first-order and second-order dissociation constants are 3.52 and 17.61, respectively, for Li2S6 dissociated into LiS6– and S62–. Simultaneously, Li2S6 can also dissociate into LiS3• radicals with dissociation constant of 7.80. The experimental ultraviolt–visible spectrum of stoichiometric 2 mM Li2S6 in DME was interpreted by the individual contributions of various polysulfide species using time-dependent density functional theory calculations. The concentrations of Li2S6 and the dissociated LiS6–, S62–, and LiS3• were further calculated for different electrolyte-to-sulfur ratios. It is found that neutral Li2S6 is dominant in DME, while polysulfide anions and radicals are rare.