Engineering 3D Lattice Oxygen Metal–Organic Frameworks for Fast-Charging Quasi-Solid-State Lithium Metal Batteries

Metal–organic frameworks (MOFs) show great promise in composite solid polymer electrolytes by simultaneously immobilizing anions and facilitating cation transport, yet the synergy between these mechanisms remains unclear. To elucidate this interplay, a series of isoreticular indium-based MOFs (InOF-1, MIL-60, and MIL-68(In)) are designed, all featuring identical In-O6 coordination centers while exhibiting systematically varies pore architectures. Among them, MIL-60 stands out by achieving an optimal balance between physical size exclusion and chemical mediation of ion transport. It's precisely engineered 6.5 Å pores effectively block bulky TFSI⁻ anions while allowing the diffusion of lithium ion (Li⁺)–solvent complexes. Concurrently, its exceptionally high lattice oxygen density (19.97 nm⁻³, confirmed by density functional theory calculations) forms a 3D fast Li⁺ conduction network, enabling barrier-free ion hopping. This dual mechanism results in superior electrochemical performance, including an ultrahigh room-temperature Li⁺ conductivity of 1.11 × 10⁻³ S cm⁻¹ at 30 °C, an unprecedented Li⁺ transference number of 0.54, and outstanding cycling stability with 95.2% capacity retention after 1800 cycles at 10 C in LiFePO₄||Li cells. This study proposes a new design strategy aligning pore size with Li⁺ transport sites to optimize ion conduction. MIL-60 exemplifies a promising model for single-ion conductors and guides next-generation solid-state batteries.