Molecular Self-Assembled Ether-Based Polyrotaxane Solid Electrolyte for Lithium Metal Batteries

Poly(ethylene oxide) has been widely investigated as a potential separator for solid-state lithium metal batteries. However, its applications were significantly restricted by low ionic conductivity and a narrow electrochemical stability window (<4.0 V vs Li/Li⁺) at room temperature. Herein, a novel molecular self-assembled ether-based polyrotaxane electrolyte was designed using different functional units and prepared by threading cyclic 18-crown ether-6 (18C6) to linear poly(ethylene glycol) (PEG) via intermolecular hydrogen bond and terminating with hexamethylene diisocyanate trimer (HDIt), which was strongly confirmed by local structure-sensitive solid/liquid-state nuclear magnetic resonance (NMR) techniques. The designed electrolyte has shown an obviously increased room-temperature ionic conductivity of 3.48 × 10^-4 S cm^-1 compared to 1.12 × 10^-5 S cm^-1 without assembling polyrotaxane functional units, contributing to the enhanced cycling stability of batteries with both LiFePO₄ and LiNi_0.8Co_0.15Al_0.05O₂ cathode materials. This advanced molecular self-assembled strategy provides a new paradigm in designing solid polymer electrolytes with demanded performance for lithium metal batteries.