Decoupling Interfacial Stability and Ion Transport in Solid Polymer Electrolyte by Tailored Ligand Chemistry for Lithium Metal Battery

Achieving fast ion transport kinetics and high interfacial stability simultaneously is challenging for polymer electrolytes in solid-state lithium batteries, as the coordination environment optimal for Li⁺ conduction struggles to generate desirable interphase chemistry. Herein, the adjustable property of organic ligands is exploited in metal–organic frameworks (MOFs) to develop a hierarchical composite electrolyte, incorporating heterogeneous and spatially confined MOF nanofillers into a poly-1,3-dioxolane matrix. The defect-engineered University of Oslo-66 MOFs (UiO-66d) with tailored Lewis acidity can separate ion pairs and optimize Li⁺ migration through weakened solvation effects, thereby enhancing ion conductivity by over sixfold (0.85 mS cm⁻¹@25 °C). At the lithium anode side, a densified University of Oslo-67 MOFs (UiO-67) layer with conjugated π electrons facilitates anion participation in the solvation sheath, promoting anion reduction and thereby forming LiF/Li₃N-dominated solid electrolyte interphase for isotropic Li deposition. The as-assembled Li||LiFePO₄ full cell delivers superior cycling stability with 92.7% of capacity retained over 2000 cycles at 2 C. Notably, the developed electrolyte demonstrates excellent compatibility with high-voltage cathodes, achieving 80% capacity retention with LiNi_0.5Co_0.2Mn_0.3O₂ over 630 cycles. This work provides valuable insights into decoupling transport and interfacial challenges in solid-state lithium batteries, paving the way for advanced battery technologies. © 2024 Wiley-VCH GmbH.