In Situ Characterizations for the Degradation Mechanism of Li‐Rich Mn‐Based Layered Oxides

With the rapid development of the economy, increasing demand for energy storage and electric vehicles require electrode materials for batteries with high energy density, safety, and cyclability, especially for lithium‐ion (Li‐ion) battery cathodes. However, the understanding of their degradation mechanism remains insufficient due to the complex battery system, the transient nature of the de/lithiation processes, and the lack of advanced characterization techniques. Among these challenges, the mechanism of the Li‐rich layered cathode family with high operating voltage and cationic‐anionic hybrid charge compensation is particularly difficult to study. For the Li‐rich family, their electrochemical mechanisms, for example, oxygen redox reaction and structural evolution, were almost impossible to completely clarify in terms of conventional characterization techniques until the development of various in situ techniques. It is obvious that advanced in situ techniques have accelerated the pace of scientific truth exploration. In this review, these intricate mechanisms revealed by various in situ techniques are summarized to clarify the failure mechanism of Li‐rich layered cathodes, and an outlook on the application of these advanced techniques within different battery systems is provided. This review highlights how in situ devices can clearly reveal complex mechanisms and further provides the consultation on characterization techniques for mechanism exploration in various research fields.