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

ABSTRACT 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/TrCuMOF 8 ) as thermally stable SSEs for LMBs. The crystal‐transformed HOF/MOF heterostructure constructs continuous low‐energy Li + transport pathways, while the pendant ‐CH 3 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/TrCuMOF 8 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/TrCuMOF 8 SSEs maintain structural integrity at high temperatures (180°C), effectively suppressing electrolyte shrinkage and thermal short‐circuit propagation. The assembled Li|HOFa/TrCuMOF 8 SSEs|LiFePO 4 LMBs achieve 97.8% capacity retention after 1000 cycles at 2 C and maintain stable cycling even at 100°C. Remarkably, the Li|HOFa/TrCuMOF 8 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.