Tailored Electrolyte Design Based on E/S Ratio for Practical Lithium-Sulfur Batteries

Abstract

Achieving high energy density in lithium–sulfur batteries (LSBs) requires operating under ultra- lean electrolyte conditions, yet the electrochemical behavior is highly sensitive to the electrolyte-to- sulfur (E/S) ratio. Despite its importance, most previous studies evaluated electrolyte compositions at a single E/S ratio, overlooking the coupled impact of electrolyte quantity and solvation characteristics. In this study, we systematically investigate how the E/S ratio determines cell polarization, sulfur redox kinetics, and lithium metal stability. The solvating power of the electrolyte is subsequently examined as a key factor controlling the solubility of polysulfides and the interfacial chemistry at both electrodes. Strong-solvating electrolytes promote rapid sulfur conversion but accelerate lithium corrosion and electrolyte depletion, while weak-solvating electrolytes suppress parasitic reactions at anode yet induce sluggish redox kinetics at lean conditions. By coupling the effects of E/S ratio and solvating power, we identify the optimal balance between E/S ratio and solvating power required for stable long-term cycling. This work provides a framework for electrolyte design in practical lean-electrolyte LSBs, highlighting the need for co-optimization of E/S ratio and solvating power to simultaneously enhance energy density and durability.