Energy Threshold of Nonlinear Sulfur Solubility for Li–S Batteries

Abstract

Unclear regulation mechanisms of solid solubility make it difficult to accurately control its concentration, posing challenges for accelerating chemical reactions. Herein, we use a model system to determine the effects of solvent type and ratio, concentration, and type of lithium salt on sulfur solubility. Our findings reveal a nonlinear relationship between sulfur solubility and both lithium salt concentration and the ratio of different solvents in composite solutions. Importantly, significant differences in sulfur solubility are discovered with changes in the solvation structure regulated by the type of salt anion. Quantitative evaluation of nonlinear sulfur solubility is illustrated to be breaking the threshold value of the interaction energy between the solute and solvent molecules. Based on these findings, simultaneous regulation of sulfur and lithium polysulfide concentrations in ether electrolytes can be achieved by controlling the concentration and type of salts. As a result, a liquid–liquid–solid reaction pathway is supported for lithium–sulfur batteries with a finite amount of electrolyte in the coin cell, and the pouch cell shows an energy density of 554 Wh kg^–1, ranking at the top level of the reported system.