Toward the Rational Design of Ion-Conducting Ionic Liquid-Incorporated Metal-Organic Framework Hybrids

Solid-state ionics have been the subject of intense research because of their possible applications as solid electrolytes for all-solid-state electrochemical devices. Ionic liquid-introduced metal-organic frameworks (IL@MOFs) are an emerging class of hybrid solids with superior ionic conductivity, in which the migration of component ions of ILs in the pores is responsible for ionic conduction. In this review, we present an overview of the development of ion-conducting IL@MOF hybrids from the perspective of synthetic methodologies to incorporate ILs into MOFs and the ion-conducting behavior controlled by the IL filling level, ion species of ILs, and MOF structures such as pore size and pore surface state. Finally, we devote attention to the Li⁺-ion conduction, especially the Li⁺-ion transport number, of the pore-encapsulated Li⁺-containing ILs directed toward applications in all-solid-state lithium-ion batteries.