The physical properties of clays and micas can be controlled by exchanging ions in the crystal lattice. Atomically thin materials can have superior properties in a range of membrane applications, yet the ion-exchange process itself remains largely unexplored in few-layer crystals. Here we use atomic-resolution scanning transmission electron microscopy to study the dynamics of ion exchange and reveal individual ion binding sites in atomically thin and artificially restacked clays and micas. We find that the ion diffusion coefficient for the interlayer space of atomically thin samples is up to 10⁴ times larger than in bulk crystals and approaches its value in free water. Samples where no bulk exchange is expected display fast exchange at restacked interfaces, where the exchanged ions arrange in islands with dimensions controlled by the moiré superlattice dimensions. We attribute the fast ion diffusion to enhanced interlayer expandability resulting from weaker interlayer binding forces in both atomically thin and restacked materials. This work provides atomic scale insights into ion diffusion in highly confined spaces and suggests strategies to design exfoliated clay membranes with enhanced performance.

粘土和云母的物理性质可以通过交换晶格中的离子来控制。原子级薄材料可以在一系列膜应用中具有优异的性能，但离子交换过程本身在几层晶体中仍未得到充分探索。在这里，我们使用原子分辨率扫描透射电子显微镜来研究离子交换的动力学，并揭示原子薄和人工重新堆叠的粘土和云母中的单个离子结合位点。我们发现原子薄样品的层间空间的离子扩散系数高达 10 ⁴比散装晶体大 1 倍，并接近其在自由水中的值。预计没有大量交换的样品在重新堆叠的界面处显示快速交换，其中交换的离子排列成岛状，尺寸由莫尔超晶格尺寸控制。我们将快速离子扩散归因于增强的层间扩展性，这是由于原子薄和重新堆叠材料中较弱的层间结合力导致的。这项工作为高度受限空间中的离子扩散提供了原子尺度的见解，并提出了设计具有增强性能的剥离粘土膜的策略。