Recent Progress in Transmission Electron Microscopy (TEM)-Based Studies of Lithium-Ion Battery Cathode Materials

Transmission electron microscopy (TEM) has played a pivotal role in elucidating the structure–property relationships of lithium-ion battery cathode materials by enabling direct observation of microstructural and atomic-scale features. In this review, recent progress in TEM-based studies of commercially relevant cathode materials—including ternary (Ni–Co–Mn) layered cathodes, lithium-rich layered oxides, and olivine-type phosphates such as LiFePO4 and LiMnₓFe₁₋ ₓPO4 - is systematically summarized. For ternary layered cathodes, TEM has been widely employed to reveal the morphology and crystallographic orientation of primary particles, elemental distribution of transition metals, dopants, and surface modifications, as well as degradation pathways associated with cation mixing and layered-to-rock-salt phase transitions. In lithium-rich layered oxides, advanced TEM and Scanning transmission electron microscopy techniques have enabled direct visualization of oxygen-related structural rearrangements, defect formation, and lattice distortions induced during electrochemical activation. In olivine-type cathodes, TEM-based analyses have provided critical insights into primary particle size, carbon coating thickness, and atomic-scale antisite defects that govern lithium-ion transport. Collectively, these studies demonstrate that TEM is not only a powerful characterization tool for probing nanoscale structures but also an indispensable technique for understanding electrochemical performance and degradation behavior, and for guiding the rational design of high-performance cathode materials. This review highlights how advances in TEM methodologies continue to deepen our understanding of cathode materials and outlines future directions for TEM-driven battery research.