A Lamellar MXene (Ti 3 C 2 T x )/PSS Composite Membrane for Fast and Selective Lithium‐Ion Separation

A two‐dimensional (2D) laminar membrane with Li + selective transport channels is obtained by stacking MXene nanosheets with the introduction of poly(sodium 4‐styrene sulfonate) (PSS) with active sulfonate sites, which exhibits excellent Li + selectivity from ionic mixture solutions of Na + , K + , and Mg 2+ . The Li + permeation rate through the MXene@PSS composite membrane is as high as 0.08 mol m −2  h −1 , while the Li + /Mg 2+ , Li + /Na + , and Li + /K + selectivities are 28, 15.5, and 12.7, respectively. Combining the simulation and experimental results, we further confirm that the highly selective rapid transport of partially dehydrated Li + within subnanochannels can be attributed to the precisely controlled interlayer spacing and the relatively weaker ion‐terminal (−SO 3 − ) interaction. This study deepens the understanding of ion‐selective permeation in confined channels and provides a general membrane design concept.