Defect-Tailoring Metal-Organic Frameworks for Highly Fast-Charging Quasi-Solid-State Electrolytes Lithium Metal Batteries

Metal-organic frameworks (MOFs) show revolutionary potential in quasi-solid-state electrolytes (QSSEs) designed for high-energy-density batteries, owing to their tunable nanoporous structures and open metal sites (OMSs). However, their application is hindered by insufficient Li⁺ dissociation and low ionic conductivity, attributed to limited metal active sites. This study employed defect engineering to modulate hafnium-based MOFs, increasing OMS density while optimizing the pore microenvironment. The engineered defects improve the Lewis acid strength of OMSs, driving lithium salt dissociation and establishing strong chemisorption of TFSI^- anions. By synergistically optimizing defect density, Lewis acidity, and structural stability, the defect-engineered Hf-MOF-QSSE achieved an ionic conductivity of 1.0 mS cm^-1 at 30 °C and delivered a critical current density of 2 mA cm^-2, surpassing previously reported MOF-QSSEs, underscoring the pivotal role of defect engineering in electrolyte optimization. Furthermore, Li||LiFePO₄ cells exhibited excellent cycling stability and ultrahigh rate capability, retaining 93% of their capacity after 1500 cycles at 10C, while Li||NCM811 cells maintained a specific capacity of 85 mAh g^-1 after 600 cycles at 5C.