Nacre-like Mechanically Robust Heterojunction for Lithium-Ion Extraction

Nanolaminate membranes composed of two-dimensional materials are promising candidates for molecular sieving via size-limited diffusion and charge effect in nanoconfinement, but these materials suffer from weak mechanical properties and instability in water due to the hydrophilicity. Here, inspired by natural nacre structure, we design an ion-gating heterojunction with opposite charges and asymmetrical nanochannels. Nanofibers and nanosheets form a typical brick-and-mortar structure, which exhibits mechanical robustness compared with other reported materials. Additionally, the heterostructure contributes to both restraining concentration polarization and generating spontaneous potential gradient. Thus, based on the confined dehydration and charge-exclusion effects, we reveal the ordered transport rank Li⁺ > Na⁺ > K⁺ > Mg²⁺ > Ca²⁺, which depends on the valence and radius of ions. Ionic gating achieves the extraction of lithium ions with the Li⁺/Na⁺ and Li⁺/K⁺ selectivity of 2.52 and 4.78. This membrane may have applications in lithium-ion batteries and designs of ion-separation membranes.