Revealing the microstructure and mechanism of layered oxide cathodes for sodium-ion batteries by advanced TEM techniques

Sodium-ion batteries (SIBs) stand as promising alternatives to current lithium-ion batteries in various energy storage fields. Despite their potential, challenges arise due to the intricate nature of large-size Na⁺ charge carriers, impacting the cycling stability and rate performance, which currently fall short of commercialization requirements. Therefore, it is crucial to gain a deeper understanding of the structural changes and chemical evolution of battery components. The advancement of transmission electron microscopy (TEM) technology enables multi-dimensional characterization and analysis of SIB cathode materials. This review offers an in-depth overview and comparison of the utilization of advanced TEM techniques for studying layered oxide cathode materials. It covers various aspects, including the common analysis of atomic structures, structural phase transitions, elemental valence tracing, and anion redox, and provides insights from current in situ TEM experiments. The presented review aims to provide valuable insights to inform the rational design of high-performance SIB cathodes.