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

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.