Ionic Conduction in Metal–Organic Frameworks with Incorporated Ionic Liquids

Encapsulation of ionic liquids (ILs) into porous materials can provide environmentally benign solid-state electrolytes for various electrochemical devices, in particular, porous metal–organic frameworks (MOFs) that enable us to tailor their framework and pore structures by varying central metals and organic linkers as well as the ILs with an unlimited number of possible cation–anion combinations. Therefore, rational materials design based on the accumulated knowledge about the relationship between materials and functionalities is essential for studying IL@MOF hybrid composites with desired properties. In this Review, we first introduce synthetic methodologies to incorporate ILs into MOFs, especially based on the postimpregnation approach. Interactions and the distribution of component ions of the ILs within the MOFs are discussed from the viewpoint of ion mobility, which is responsible for the performance of electrochemical devices. Finally, we devote attention to the ion-conducting properties, including lithium ion, proton, and hydroxide conductions, of the hybrid composites.