Highly Solvating Electrolytes with Core-Shell Solvation Structure for Lean-Electrolyte Lithium-Sulfur Batteries

Abstract

The practical energy density of lithium-sulfur batteries is limited by the low sulfur utilization at lean electrolyte conditions. The highly solvating electrolytes (HSEs) promise to address the issue at harsh conditions, but the conflicting challenges of long-term stability of radical-mediated sulfur redox reactions (SRR) and the poor stability with lithium metal anode (LMA) have dimmed the efforts. We now present a unique core–shell solvation structured HSE formulated with classical ether-based solvents and phosphoramide co-solvent. The unique core–shell solvation structure features confinement of the phosphoramide in the first solvation shell, which prohibits severe contact reactions with LMA and endows prolonged stability for [S₃]⋅⁻ radical, favoring a rapid radical-mediated solution-based SRR. The cell with the proposed electrolyte showing a high capacity of 864 mAh g_sulfur⁻¹ under high sulfur loading of 5.5 mg_sulfur cm⁻² and low E/S ratio of 4 μL mg_sulfur⁻¹. The strategy further enables steady cycling of a 2.71-A h pouch cell with a high specific energy of 307 W h kg⁻¹. Our work highlights the fundamental chemical concept of tuning the solvation structure to simultaneously tame the SRR and LMA stability for metal-sulfur batteries wherein the electrode reactions are heavily coupled with electrolyte chemistry.