Supramolecular deep eutectic electrolytes with quasi-single-ion conduction for stable high-voltage lithium metal batteries

Lithium metal batteries (LMBs) promise ultrahigh energy density, but deep eutectic electrolytes (DEEs) suffer from intrinsically low lithium-ion transference numbers ( ), an overlooked weakness that exacerbates concentration polarization and interfacial instability, especially under high-voltage operation. Here, we report a supramolecular DEE comprising 18-crown-6 (18C6) and lithium nonafluorobutanesulfonate (LiNFSA) that achieves quasi-single-ion conduction ( = 0.88) and a 5.3 V stability window—benchmarks unprecedented for DEEs. Results reveal that the Li + –18C6 chelation, combined with the bulky, charge-delocalized and geometrically mismatched NFSA - anion, suppresses correlated cation–anion migration, resulting in high- conduction. The optimized electrolyte (LNC-2.5) enables uniform LiF-rich solid–electrolyte interphases and cathode–electrolyte interphases, effectively mitigating dendrite growth, side reactions, and transition-metal dissolution. In high-voltage LMBs, it enables long-term cycling stability and low polarization, with nearly 100% capacity retention over 450 cycles using LiMnFePO 4 cathodes, while maintaining broad compatibility with LiCoO 2 , LiFePO 4 , organic cathodes, and pouch-cell configurations. This work establishes a supramolecular design principle to couple selective Li + transport with interfacial durability for safe, high-performance LMBs. • Introduces a universal dual supramolecular and anion-engineering design principle for achieving high- electrolytes. • Demonstrates a of 0.88 with 5.3 V electrochemical stability, a record high among all reported DEEs. • LNC-2.5 promotes the formation of LiF-enriched SEIs and CEIs, resulting in stable interphases and high-voltage compatibility.