Lanthanum-Enriched PEO-Based Composite Electrolytes Inducing Interface Passivation and the Ion-Sieving Effect

Poly(ethylene oxide) (PEO)-based solid electrolytes are key to developing safe and high-energy all-solid-state lithium metal batteries, but they suffer from low ionic conductivity, strong Li⁺-anion association, and insufficient oxidative stability at increased voltages. In this study, a lanthanum-enriched PEO composite electrolyte (LP) was designed by incorporating lanthanum formate molecular clusters (LaMe) as multifunctional Lewis acid sites to achieve simultaneous enhancement of ion transport and interfacial stability. The La-O coordination framework strongly anchors TFSI^- anions while repelling Li⁺, effectively suppressing Li⁺-TFSI^- association and facilitating Li⁺ dissociation and migration. Density functional theory (DFT) calculations confirm the reduced binding energy, redistributed electrostatic potential, and formation of low-barrier Li⁺ migration pathways. Consequently, the LP electrolyte exhibits a high ionic conductivity of 1.67 × 10^-4 S cm^-1 at 30 °C, a Li⁺ transference number of 0.57, and an extended electrochemical stability window of up to 4.5 V. Li||Li symmetric cells deliver stable plating/stripping behavior for more than 2000 h with low polarization, while Li||LFP full cells maintain 94.61% capacity retention after 300 cycles at 0.5 C and operate stably up to 1000 cycles at 4.2 V. The synergistic effects of anion anchoring, polymer activation, and stable LiF-rich interphase formation enable the LP electrolyte to achieve high-voltage tolerance, dendrite-free cycling, and excellent long-term durability, offering a promising strategy for next-generation solid-state lithium metal batteries.