Stabilizing Lithium-Sulfur Batteries in Carbonate Electrolytes via DODT-PEG Interphase Engineering and Ultramicroporous Carbon Confinement.

Stabilizing lithium-sulfur batteries in carbonate-based electrolytes requires simultaneous control over sulfur behavior and interfacial chemistry. In this work, we present a cooperative strategy that combines a poly-(vinylidene fluoride) (PVDF)-derived ultramicroporous carbon (UMC) sulfur host with a 3,6-dioxa-1,8-octane-dithiol -poly-(ethylene glycol) (DODT-PEG) copolymer electrolyte additive to address these challenges in a unified manner. The ultramicroporous structure of UMC physically confines sulfur species within subnanometer pores, limiting polysulfide formation and outward diffusion, while the DODT-PEG copolymer modifies the cathode/electrolyte interphase to promote ion-conductive pathways and stabilize sulfur redox reactions. Through structural, electrochemical, impedance, and postmortem analyses, the distinct roles of sulfur confinement and interphase regulation are identified and correlated with improved electrochemical behavior. The combined system enables high reversible sulfur utilization, stable cycling with a Coulombic efficiency of >99%, and enhanced rate capability. Li//Li symmetric cell analysis further reveals that the beneficial effect of the copolymer additive is localized at the cathode rather than at the lithium surface. This work demonstrates that coordinated host design and electrolyte engineering provide a simple and scalable route for improving Li-S battery performance in conventional carbonate electrolytes.