Competitive Coordination to Ether Oxygens Enables High-Ionic-Conductivity Solid Polymer Electrolytes at Room Temperature.

The practical application of poly(ethylene oxide) (PEO) electrolytes in solid-state lithium metal batteries is severely constrained by low ionic conductivity at ambient temperature. To address this intrinsic limitation, we introduce FeF3 as a multifunctional additive into the PEO/poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF‑HFP) matrix, yielding the FeF3‑PEOPVLi electrolyte. Fe3+ ions with strong Lewis acidity competitively coordinate with the ether oxygen atoms via Fe3+-O-C interactions, thereby weakening the native Li+-O-C coordination and substantially reducing the energy barrier for Li+ hopping. Concurrently, the strong electron withdrawing nature of Fe3+ promotes lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dissociation by weakening the Li-N bond, increasing the concentration of free Li+ ions available for ionic transport. Benefiting from these synergistic effects, the FeF3‑PEOPVLi electrolyte achieves high ionic conductivity of 0.13 mS cm- 1 at 25°C. Solid-state Li||LiFePO4 batteries deliver discharge capacity of 120.6 mAh g- 1 at 0.5 C at 25°C and retains 88.4% of its capacity after 1000 cycles. This work demonstrates that rational modulation of the coordination environment within PEO provides a viable and effective pathway toward high‑performance room‑temperature solid‑state lithium metal batteries.