Porous Liquids as Electrolyte: A Case Study of Li⁺ and Mg²⁺ Ion Transport in Crown Ether-Based Type-II Porous Liquids

We demonstrated an enhanced ion transport properties of type-II porous liquid-based electrolyte in which crown ether provides internal porosity and are capable of coordinating and transporting Li+ and Mg2+ ions. We investigated the solvation structure and transport properties of the porous liquid electrolytes with different functional groups and cavity sizes. Among the electrolytes studied, the 12-crown-4 (12C4)-based porous liquid electrolyte exhibited the most enhanced ionic conductivity due to size match between the crown ether cavity and the Li+ ion. Nuclear magnetic resonance and Fourier transform infrared analyses revealed that addition of crown ethers reduces the Li+ ion–solvent interaction, resulting in the formation of Li-crown ether complexes. Molecular simulations complement such observations by describing the detailed solvation environment at molecular scale, including complexation between Li+ and Mg2+ ions and 12C4. The strategy described here using crown ether-based porous liquids should be applicable to design versatile electrolytes for various metal-ion batteries.