An ionic-liquid functionalized metal–organic framework and its high performance as a solid electrolyte for lithium-ion conduction

Crystalline porous metal-organic frameworks (MOFs) have attracted great interest, including in the field of solid-state electrolytes. Herein, we report a new type of solid-state electrolyte based on an MOF matrix and a Li⁺ ionic liquid. By covalently bonding the Li⁺ ionic liquid (MIMS·LiTFSI) on the stable UiO-67 framework, the obtained crystalline IL_Li-MOF material exhibited high ion conductivities within a wide temperature range (30 °C 1.62 × 10^-3 S cm^-1, 110 °C 1.26 × 10^-2 S cm^-1) and efficient Li⁺ transport (<i>t</i>_Li⁺ = 0.88) [MIMS: 1-(1-mthyl-3-imidazolio) propane-3-sulfonate, LiTFSI: lithium bis(trifluoromethane sulfonyl)imide]. Characterization and control experiments demonstrated the ordered structure of the ionic-liquid moiety (MIMS·LiTFSI) arranged along the infinite channels, with the ultramicropores (<1 nm) in the MOF well accounting for the high and efficient targeted Li⁺ transfer. Additionally, this two-in-one strategy endows the crystalline electrolyte with desirable advantages, such as inflammable properties, stability and no leakage. The structure, electrochemical properties and ion conduction mechanism of the IL_Li-MOF were investigated and discussed. We hope that this work will provide a new strategy for the design and synthesis of high-performance solid-state electrolytes for lithium-ion batteries.