Ion–Dipole Interaction Engineering in Weakly Solvated Polymer Electrolytes for Stable Li-O2 Batteries

Abstract

The development of lithium-oxygen (Li-O2) batteries, which possess high theoretical energy density, has long been hindered by safety issues and parasitic reactions arising from conventional liquid electrolytes. Gel polymer electrolytes (GPEs) have emerged as a promising alternative to settle these issues; however, their practical application is still limited by poor interfacial compatibility and insufficient oxidative stability. Herein, we design GPEs that uniquely integrate a weakly solvating siloxane network, 3-(trimethoxysilyl)propyl methacrylate (MAPTMS), with a polar carbonate matrix of vinyl ethylene carbonate (VEC) via in situ copolymerization. The siloxane framework enhances structural stability and interfacial compatibility, while polar side chains promote efficient ion dissociation and transport. The optimized poly(VEC-co-MAPTMS) (PMVL) electrolyte exhibits a high ionic conductivity of 0.255 mS cm–1 at room temperature and an electrochemical stability window up to 4.96 V. Combined spectroscopic characterization and molecular dynamics (MD) simulations reveal that MAPTMS incorporation modulates polymer crystallinity and Li+ coordination environments, driving the formation of abundant aggregate (AGG) microdomains. This anion-rich solvation structure not only accelerates ion transport and lowers the Li+ desolvation barrier to enable uniform lithium deposition but also steers the formation of a thin, inorganic-rich solid electrolyte interphase (SEI). Leveraging this anion-rich solvation environment, a symmetric cell with PMVL achieves an extended cycle life of 4000 h at 0.1 mA cm–2 and 0.1 mAh cm–2 capacity. Furthermore, the Li-O2 battery using PMVL delivers stable operation for 140 cycles at 25 °C under a fixed capacity of 500 mAh g–1. This work demonstrates that the molecular-level synergy between weakly solvating and strongly polar segments offers a universal strategy to concurrently address ionic conductivity, interfacial stability, and oxidation resistance challenges in high-energy-density polymer electrolyte batteries.