Engineering the d-Orbital Energy of Metal–Organic Frameworks-Based Solid-State Electrolytes for Lithium–Metal Batteries

Having an orbital-level understanding of the relationship between the electronic state of a central metal in metal–organic frameworks (MOFs) as solid-state electrolytes (SSEs) and Li + ion conductivity is crucial yet challenging for lithium–metal batteries (LMBs). In this study, we report the synthesis of functionalized UiO-66 as a model system to investigate the relationship between the d-band energy of Zr 3d orbitals and Li + ion conductivity. Specifically, the NO 2 group in electron-withdrawing NO 2 -decorated UiO-66 (NO 2 -UiO-66) can capture electron from ZrO 8 sites, resulting the increased energy in 3d z 2 and 3d xz /yz orbitals of Zr atom. The high-energy 3d z 2 and 3d xz /yz orbitals of Zr in NO 2 -UiO-66 hybridize with the 2p z and 2p x/y orbitals of O in ClO 4 –, leading to decreased antibonding orbital energy and resulting in a strong adsorption, ultimately immobilizing the anions and enhancing ion conductivities. Establishing the correlation between the d-orbital energy and Li + ion conductivity may create a descriptor for designing efficient SSEs for LMBs.