A Bioinspired Membrane with Ultrahigh Li⁺/Na⁺ and Li⁺/K⁺ Separations Enables Direct Lithium Extraction from Brine

Membranes with precise Li⁺/Na⁺ and Li⁺/K⁺ separations are imperative for lithium extraction from brine to address the lithium supply shortage. However, achieving this goal remains a daunting challenge due to the similar valence, chemical properties, and subtle atomic-scale distinctions among these monovalent cations. Herein, inspired by the strict size-sieving effect of biological ion channels, a membrane is presented based on nonporous crystalline materials featuring structurally rigid, dimensionally confined, and long-range ordered ion channels that exclusively permeate naked Li⁺ but block Na⁺ and K⁺. This naked-Li⁺-sieving behavior not only enables unprecedented Li⁺/Na⁺ and Li⁺/K⁺ selectivities up to 2707.4 and 5109.8, respectively, even surpassing the state-of-the-art membranes by at least two orders of magnitude, but also demonstrates impressive Li⁺/Mg²⁺ and Li⁺/Ca²⁺ separation capabilities. Moreover, this bioinspired membrane has to be utilized for creating a one-step lithium extraction strategy from natural brines rich in Na⁺, K⁺, and Mg²⁺ without utilizing chemicals or creating solid waste, and it simultaneously produces hydrogen. This research has proposed a new type of ion-sieving membrane and also provides an envisioning of the design paradigm and development of advanced membranes, ion separation, and lithium extraction.