Deciphering the Dynamic Balance Between Solvation Strength and Polysulfides Reaction Heterogeneity in Practical...

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 S⁴⁺-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.