Ion exchange is a longstanding and naturally occurring phenomenon in which ions are exchanged between a solid material A and a media B while preserving charge balance. This process is vital for modern technology and daily life, playing a crucial role in water purification, pharmaceuticals, and energy storage. It serves as a key mechanism in material synthesis, enabling precise control over compositions and properties. Additionally, ion exchange is widely employed in element separations, such as rare-earth purification and alkali-metal recovery, due to its high selectivity and efficiency. Its versatile applications underscore its significance in advancing scientific and industrial progress.

This dissertation focuses on the intrinsic ion exchange behavior in layered oxides and provides the insights into the ion exchange phenomenon from fundamental understanding and show the versatile possibilities by utilizing ion exchange in materials synthesis and element separation field. In Chapter 2, we studied the Li/Na exchange in layered oxides materials by using model CoO₂ materials. We show that the Li/Na exchange process is governed by two-phase equilibrium due to the intrinsic different structural preference to Li and Na ions of layered oxides. In Chapter 3, we continue the study of Li/Na exchange in layered oxides and show the two-phase equilibrium governed exchange pathway is a very general exchange pathway among different transition metal layered oxides. We also demonstrated that the ion migration pathway controlled by the structural preference is the determination factor on phase separation or “intermediate phase” behaviors. In Chapter 4, we study the potential of rare earth element separation by utilizing ion exchange behavior in hydrated layered V₂O₅. We show the hydrated layered V₂O₅ can host rare earth ions with their intact first hydration shell, and at the same time provide the large enough distinguishing capability towards different rare earth ions. In Chapter 5, we provide a short perspective to indicating the possible future research direction in terms of ion exchange in the applications of materials synthesis and element separation.