In Situ TEM Studies on Electrochemical Mechanisms of Rechargeable Ion Battery Cathodes

Due to recent developments in secondary ion batteries for high‐energy‐density applications, a thorough understanding of the underlying mechanism of advanced cathode materials is of vital importance. In situ transmission electron microscopy (TEM) techniques capable of high spatial and temporal resolution in operando analysis of dynamic battery systems have attracted significant interest. However, the complex electrochemical reaction mechanisms of cathode materials have not been extensively investigated using in situ TEM due to technical difficulties in implementation. This perspective provides an overview on the recent development of in situ TEM for studying representative layered and olivine‐type cathode materials in secondary ion batteries; it further discusses the critical challenges and possible breakthroughs of this technique in deepening fundamental understandings in the near future.