Modulating Li⁺ and Polysulfide Solvation with Low-Density Moderately Solvating Electrolytes for Lithium-Sulfur...

Lithium-sulfur (Li-S) batteries show great promise as the next-generation rechargeable batteries, yet they still suffer from polysulfide shuttling and interphasial instability. Electrolyte, as the medium for ion transport and sulfur conversion, plays a crucial role in overcoming these challenges. Here, we introduce a moderately solvating electrolyte (MSE) based on low-density, low-viscosity, and nonfluorinated ether co-solvents that balances polysulfide suppression, Li metal stabilization, and redox kinetics. Through multiple solvent-solvent and solvent-ion interactions, the optimized MSE weakens Li⁺-solvent pairing while strengthening cation-anion interactions, thereby lowering the desolvation barrier and promoting the formation of a favorable solid-electrolyte interphase (SEI). Meanwhile, MSE limits the polysulfide dissolution but improves the accessibility of active material through better wettability and tailored solvation environment, leading to an altered sulfur deposition mechanism with β - α conversion. This approach enables a stable cycling of high-mass loading Li-S cells (> 3.5 mg cm^-2) at both room temperature and 45 °C (where shuttling and side reactions are severer), and demonstrates a pouch cell with lean electrolyte content (4.5 µL mg s^-1). This work highlights a practical route to develop high-performance electrolyte for Li-S cells and provides mechanistic insights into their operation.