Mechanistic understanding of a bifunctional carbonate additive for enhanced performance in lithium-sulfur battery

Lithium-sulfur (Li-S) batteries stand promising for next-generation energy storage systems due to their high specific capacity and cost-effectiveness. However, their commercialization is hindered by sluggish sulfur reduction reaction (SRR) kinetics and polysulfide migration. To address these challenges, we introduce bis(4-nitrophenyl) carbonate (BNC) as a bifunctional electrolyte additive . At an optimal concentration, BNC leverages its polar nature to anchor soluble polysulfides while simultaneously modifying the Li + solvation structure at the molecular level, enhancing SRR kinetics. This dual functionality is confirmed through molecular dynamics simulations and electrochemical analyses . In situ electrochemical impedance spectroscopy (EIS) further shows that optimal BNC concentration reduces activation energy for polysulfides formation by 40.6%. Operando spectroscopic techniques, including Raman and X-ray absorption spectroscopy (XAS), demonstrate BNC's dual effect, with a focus on the middle-chain polysulfides conversion, supported by detailed polysulfide quantification. X-ray fluorescence (XRF) mapping reveals decreased sulfur deposition on lithium, indicating the effectiveness of shuttle suppression. These effects contribute to outstanding cycling performance under practical conditions, achieving 650.93 mAh g sulfur -1 and coulombic efficiency of 93% over 200 cycles at a C-rate of C/2. This work not only offers valuable insights into the use of unconventional carbonate-based additives but also provides a blueprint for advancing Li-S battery designs through targeted solvation structure modifications.