Deciphering the Dynamic Balance Between Solvation Strength and Polysulfides Reaction Heterogeneity in Practical Lithium‐Sulfur Batteries

ABSTRACT Achieving stable interfacial chemistry in lithium–sulfur batteries under practical conditions remains a key barrier to commercialization. Here, we demonstrate that interfacial dynamics can be effectively regulated by coupling solvation‐power control with intrinsic heterogeneity of sulfur redox chemistry through the introduction of a weakly solvating fluorinated cosolvent, LIB 1200ET (1200ET). Compared with conventional fluorinated ethers, 1200ET efficiently shifts Li ⁺ solvation environment toward a more non‐coordinated configuration at low volume fractions, enabling substantial solvation modulation without significantly impairing sulfur redox kinetics. This solvation transition weakens Li ⁺ –solvent interactions while strengthening Li ⁺ –anion and Li ⁺ –lithium polysulfide (LPS) coordination, suppressing LPS solubility and promoting reconstruction of solid–electrolyte interphase (SEI). Regulated LPS chemistry, together with 1200ET, leads to formation of a S ⁴⁺ ‐rich, LiF‐reinforced SEI with enhanced ionic conductivity and mechanical robustness. Spatially resolved sulfur K‐edge X‐ray absorption spectroscopy on pouch cells reveals pronounced current‐density‐dependent chemical heterogeneity, distinguishing kinetically dominated and solvation‐controlled regions. Under practical conditions (3.7 mg cm ⁻² sulfur loading, E/S = 6 µL mg ⁻¹ ), a single‐layer pouch cell delivers 527 mAh g ⁻¹ over 200 cycles at C/3, while an Ah‐level multilayer pouch cell achieves an energy density of 358 Wh kg ⁻¹ . These results establish non‐coordinating cosolvent‐driven solvation engineering as a scalable strategy for practical Li–S batteries.