Halogen‐Driven Ion Transport Homogenization in 3D Hierarchical MOF for Ultrastable Solid‐State Lithium Metal Batteries

Abstract Solid‐state lithium metal batteries (SSLMBs) are hindered by limited ionic conductivity, heterogeneous lithium flux and interfacial instability of solid‐state electrolytes. Herein, we report a hierarchical ion‐transport network formed by confining lithium halides (LiX, X═Cl, Br, I) within the mesoporous cages of MIL‐100(Al), synergistically integrated with a PVDF‐HFP polymer matrix. The 3D interconnected pores (0.5–1 nm) of MIL‐100(Al) not only spatially confine anions via size‐selective sieving but also enable continuous Li⁺ transport through tunable host–guest interactions between the Lewis‐acidic metal nodes and lithium halides. Among these, the LiI‐embedded composite (E‐LiI) exhibits a high Li⁺ transference number (0.88 at 25 °C) and favorable interfacial kinetics, attributed to strong anion coordination and homogeneous Li⁺ plating. Structural characterizations confirm uniform LiX distribution within the MOF framework. In addition, density functional theory (DFT) calculations and COMSOL simulation elucidate halogen‐dependent desolvation energetics and Li + transport kinetics. SSLMBs employing E‐LiI electrolytes demonstrate exceptional cycling stability (capacity retention ∼100% after 600 cycles at 2C) with high‐voltage cathodes and wide‐temperature adaptability. This work advances the rational design of multi‐scale ion‐conductive frameworks and the pivotal role of lithium halide in regulating Li deposition kinetics, offering a transformative strategy for high‐energy‐density solid‐state battery systems.