Visualizing Electrochemical Reactions in Rechargeable Battery Anodes via In Situ Transmission Electron Microscopy Study.

Rechargeable batteries are increasingly constrained by performance and safety limitations originating from anode degradation, including lithium dendrite-induced short circuits, bulk phase transformations, and interfacial SEI evolution. These processes are highly dynamic, strongly coupled, and span multiple spatial and temporal scales, complicating the establishment of direct structure-property correlations and impeding the rational design of next-generation anodes. Transmission electron microscopy (TEM), particularly in situ modalities, overcomes these limitations by combining sub-ångström resolution with multimodal capabilities-including real-space imaging, diffraction, and spectroscopy-to directly visualize morphology, structural, and chemical in real time. This review summarizes mechanistic insights obtained through analytical TEM across three hierarchical domains: (1) electrode surfaces, revealing deposition/stripping kinetics and dendrite nucleation; (2) bulk phases, tracking phase transformations, volumetric changes, and ion transport; and (3) electrode-electrolyte interfaces, elucidating SEI formation, evolution. Methodological challenges, such as electron-beam-induced artifacts, lithium's low atomic number, and liquid-phase confinement, are critically assessed, alongside emerging solutions including cryogenic TEM, low-dose imaging, and advanced liquid-cell designs. By integrating materials science with state-of-the-art electron microscopy, this review establishes a framework for leveraging in situ TEM to accelerate the development of durable, high-performance, and safe battery anodes.