Leveraging polymer backbone dynamics to tune lithium-magnesium selectivity in hydrated polymer membranes

Membrane-based separations are promising for efficiently extracting critical minerals, such as lithium. However, to replace conventional techniques, it is necessary to design membrane-materials with good selectivity for lithium over problematic contaminants such as magnesium. In this work, we synthesize a series of membrane materials with independent control over water content and polymer backbone dynamics/glass transition temperature. We characterize lithium chloride and magnesium chloride permeability, sorption, and diffusivity, and demonstrate tunability of relevant transport properties. Coarse-grained molecular dynamics simulations are used to provide further insight into the origins of the experimental trends and demonstrate the importance of cation-solvent coordination strength on cation diffusivity.