Abstract
Tunnel-structured materials have garnered significant attention as promising candidates for high-performance rechargeable batteries, owing to their unique structural characteristics that facilitate efficient ionic transport. However, understanding the dynamic processes of ionic transport within these tunnels is crucial for their further development and performance optimization. Analytical in situ transmission electron microscopy (TEM) has demonstrated its effectiveness as a powerful tool for visualizing the complex ionic transport processes in real time. In this review, we summarize the state-of-the-art in situ tracking of ionic transport processes in tunnel-structured materials for alkali metal-ion batteries (AMIBs) by TEM observation at the atomic scale, elucidating the fundamental issues pertaining to phase transformations, structural evolution, interfacial reactions and degradation mechanisms. This review covers a wide range of electrode and electrolyte materials used in AMIBs, highlighting the versatility and general applicability of in situ TEM as a powerful tool for elucidating the fundamental mechanisms underlying the performance of AMIBs. Furthermore, this work critically discusses current challenges and future research directions, offering perspectives on the development of next-generation battery materials through advanced in situ characterization techniques.