Multi‐Li + Coordination for Superior Room‐Temperature Ionic Conductivity in PEO Solid Electrolytes

ABSTRACT Ion transport in poly(ethylene oxide) (PEO) electrolytes is severely constrained by sluggish Li + mobility arising from tight chelation of ether oxygens, and by insufficient lithium salt dissociation. Inspired by polycarboxylate ether (PCE) superplasticizers in cement, we demonstrate phosphonate‐functionalized PCE (P‐PCE) could overcome both limitations. The electron‐rich ‐PO 3 2– groups could liberate Li + from the strong Li + ‐PEO chelation and promote efficient salt dissociation without trapping Li + . Instead, they facilitate rapid Li + migration through a unique multi‐Li + coordination mechanism, where the electrostatic repulsion among multiple Li + ions coordinated to a single ‐PO 3 2– destabilizes solvation and promotes rapid Li + hopping between adjacent sites. Meanwhile, P‐PCE suppresses PEO crystallization and, through multi‐Li + coordination, induces a more extended conformation of PEO, which fosters high‐entropy Li + coordination environments involving TFSI – , ether oxygens, and ‐PO 3 2– in transient combinations, promoting long‐range Li + transport. The simultaneously enhanced Li + concentration and mobility lead to a high ionic conductivity (1.7 × 10 −4 S cm −1 , 30°C) without adding liquid plasticizers. Correspondingly, Li||LiFePO 4 cells deliver high capacities of 140.6 mAh g −1 at 0.5 C and 119.7 mAh g −1 at 1 C (30°C). This work provides a simple yet effective strategy for developing high‐performance solid‐state batteries and molecular‐level insights for rational polymer electrolyte designs.