Design Principles of Crystal-Transformed HOF/MOF Heterostructures for Stable Solid-State Lithium Metal Batteries

The rational design of solid-state electrolytes (SSEs) with high ionic conductivity, interfacial robustness, and thermal stability remains a critical challenge for lithium metal batteries (LMBs). Herein, we established the crystal-transformed hydrogen-bonded organic framework/trinuclear Cu cluster organic framework heterostructures (HOFa/TrCuMOF₈) as thermally stable SSEs for LMBs. The crystal-transformed HOF/MOF heterostructure constructs continuous low-energy Li⁺ transport pathways, while the pendant -CH₃ with strong steric hindrance induces anion adsorption to effectively suppress TFSI^- migration. Meanwhile, coordination-confined TrCu synergizes with imine (C = N) groups to create a dynamically polarized local electronic environment through Li⁺-induced charge redistribution, thereby promoting selective Li⁺ transport. Consequently, the HOFa/TrCuMOF₈ SSEs deliver a high Li⁺ transference number (0.94) and ionic conductivity (2.7 mS cm^-1 at 30°C). Compared with polypropylene (PP) separators, the flexible HOFa/TrCuMOF₈ SSEs maintain structural integrity at high temperatures (180°C), effectively suppressing electrolyte shrinkage and thermal short-circuit propagation. The assembled Li|HOFa/TrCuMOF₈ SSEs|LiFePO₄ LMBs achieve 97.8% capacity retention after 1000 cycles at 2 C and maintain stable cycling even at 100°C. Remarkably, the Li|HOFa/TrCuMOF₈ SSEs|NCM811 pouch cell exhibits an impressive energy density of 259.4 Wh kg^-1 with enhanced thermal safety. This work provides a crystal-transformation strategy for engineering HOF/MOF heterostructures toward thermally stable solid-state lithium batteries.