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

ABSTRACT 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 FeF 3 as a multifunctional additive into the PEO/poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‑HFP) matrix, yielding the FeF 3 ‑PEOPVLi electrolyte. Fe 3+ ions with strong Lewis acidity competitively coordinate with the ether oxygen atoms via Fe 3+ –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 Fe 3+ 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 FeF 3 ‑PEOPVLi electrolyte achieves high ionic conductivity of 0.13 mS cm − 1 at 25°C. Solid‐state Li||LiFePO 4 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.