Decoding polarity gradient enabled ultra-high lithium ion conduction

ABSTRACT The operational stability of lithium-ion batteries under extreme cryogenic conditions remains fundamentally constrained by solvation structure heterogeneity in conventional electrolytes, where imbalanced coordination fields between high- and low-polarity solvents exacerbate desolvation barriers and interfacial ion transport resistance. Herein, this study introduces a polarity-gradient engineering (PGE) paradigm that systematically resolves solvent polarity disparity (ΔD) through atomic-scale electronic modulation. By substituting carbon with sulfur in carbonate skeletons, an 83% reduction in dielectric heterogeneity is reached (Δε = 17.1 vs. 86.6 in carbonates), enabling balanced Li⁺ coordination among cyclic/linear sulfites and anions. This homogenized solvation feature significantly accelerates desolvation kinetics (34.97 kJ·mol⁻1 activation energy vs. 79.1 kJ·mol⁻¹ in carbonates) and promotes the formation of LiF-rich interphase. Benefiting from these, the optimized electrolyte demonstrates liquid operation down to −110°C with 1 mS·cm⁻1 at −80°C, thus enabling 450 Wh·kg−1 LiCoO2/Li pouch cells to perform stable cycling at −20°C with 81% capacity retention over 400 cycles, with 73% of room-temperature capacity at −60°C. The homogeneous solvation structure intrinsically couples thermodynamic stability with accelerated interfacial kinetics, revealing a paradigm for extreme-condition energy storage. This study pioneers a universal design framework that decouples the trade-off between desolvation barriers and ion mobility, delivering an atomic-scale blueprint for cryogenic batteries.