(167y) Engineering the Enhanced Li+/Na+ Separation Efficiency through Ionic Liquid Swollen Block Copolymer Membranes

Lithium (Li) is a key component for the Li-ion batteries desired for sustainable energy storage devices. However, the separation of Li from natural sources is a very costly and laborious process. Membrane separations can potentially provide alternate means for the cost-effective and scalable separation of Li from mixed solutions. However, the separation efficiency of membrane-based Li separation is usually low, owing to the similar size of the ions such as sodium (Na) and magnesium. Here, we demonstrate enhanced separation of Li vs Na using ionic liquid swollen block copolymer membranes. We observe that the ionic liquid is confined to one of the blocks of the block copolymer and the membranes can be designed with high loading of ionic liquids. These ‘gel’ phase block copolymer domains embedded in the glassy matrix are responsible for the permeation of water, which is confirmed by no water permeation in the ionic-liquid free glassy block copolymer films. Furthermore, the presence of these ionic liquid-polymer domains introduces charge-based repulsions, thereby rejecting ~40-50% NaCl. However, these membranes reject LiCl ~2-5%, thus resulting in the enhanced selectivity of Li permeation over Na. We believe these membranes would serve as a platform for other ion separations as well.