The Origins of Ion Conductivity in MOF-Ionic Liquids Hybrid Solid Electrolytes

Fast Li⁺ solid ion conductors are a key component of all-solid-state batteries, a technology currently under development. The possible use of metallic lithium as active material in solid-state batteries warrants a quantum step improvement of battery specific energy, enabling further electric vehicles application. Hereby, we report the synthesis and ion conduction properties of a new solid hybrid electrolyte based on the MIL-121 metal organic framework (MOF) structure. After an ion exchange procedure that introduces Li⁺ in the structure, a known quantity of a soaking electrolyte is incorporated. The soaking electrolyte is based on the EMIM-TFSI ionic liquid, thus we can classify our formulation as a MOF–ionic liquid hybrid solid electrolyte. Electrical conductivity is investigated by impedance spectroscopy and preliminary studies of ion dynamics are conducted by ⁷Li NMR. The field of MOF-based ion conductors remains in incipient stages of research. Our report paves the way towards the rational design of new solid-state ion conductors.