Demand for lithium is soaring to satisfy the expanding needs of electric vehicle battery manufacturers. The extraction of this metal from brines currently relies on a time-consuming evaporation process, but a new approach devised by researchers from the University of California Santa Barbara and the University of Texas Austin may offer a more energy-efficient separation option with higher throughput.

Conventional polymer membranes previously designed to separate solutes allow sodium ions to permeate at a greater rate than lithium. A new polymer membrane synthesized by the researchers features reverse permeability selectivity and prefers lithium over sodium by a factor of roughly 2.3. The membrane contains crown ethers, which are chemically functionalized ligands that target and bind certain ions. These ligands hinder the permeation of sodium and enable lithium to pass through the membrane at a greater rate than sodium.

Overview of the materials and solvent casting process used to create 12C4-containing polynorbornene membranes. Source: Samuel J. Warnock et al.

The membrane detailed in PNAS could find application in extracting lithium from produced water in the oil and gas sector and in removing toxic constituents from water and wastewater.