Deep Dehydrated Layered Vermiculite Membrane for Selective Lithium Separation

ABSTRACT Two‐dimensional (2D) layered membranes hold great promise in water treatment due to their simple film formation, tunable interlayer spacing, and designable surface chemistry. However, their practical application of aqueous ion sieving is largely constrained by swelling problems. Here, we report a deep dehydration strategy to suppress reswelling after ion‐intercalation by removing free and bound water within the interlayer channels. The deep dehydration drives the interlayer free spacing below a critical threshold, enhancing van der Waals and electrostatic interactions, thereby energetically inhibiting rehydration and stabilizing the intercalated ions. Additionally, the intercalated ions can further enhance mono/divalent ion selectivity by reducing the transport energy barrier of monovalent ions. The resulting deeply dehydrated vermiculite membranes exhibit exceptional anti‐swelling properties, maintaining narrow interlayer channels that enable high Li + /Mg 2+ selectivity over long‐term operation. These attributes allow for the extraction of lithium from salt‐lake water, facilitating the production of industrial‐grade Li 2 CO 3 via an integrated electrodialysis–precipitation process. Notably, the membrane shows minimal water crossover under high osmotic pressure, reducing freshwater consumption. The deep dehydration strategy is not limited to vermiculite but demonstrates broad generalizability to other 2D materials, offering a universal and effective route to address the major challenge of ion sieving in complex aqueous environments.