Decoding polarity gradient enabled ultra-high lithium ion conduction
Yuqing Chen, Aiping Wang, Yun Zhao, Wei Wang, Robert Dominko, Peitao Xiao, Peng Gao, Yan Duan, Baohua Li, Xiangming He, Jilei Liu
Abstract
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.