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

Abstract 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 + /Mg 2+ and Li + /Ca 2+ 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 Mg 2+ 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.