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

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.