Atomic-scale STEM characterization of Li-ion battery materials using orientation-controlled single-crystalline specimens.

Active materials in Li-ion batteries often undergo local structural changes during the (de)lithiation process, which can strongly influence their electrochemical performance. Scanning transmission electron microscopy (STEM) is a powerful tool for investigating these changes because of its atomic-scale spatial resolution. However, atomic-resolution analysis of conventional powder samples, typically obtained from disassembled batteries, is often limited by observation directions that deviate from the low-index zone axes and overlap with other battery components. This Mini Review introduces an alternative approach based on orientation-controlled single-crystalline lamellae prepared from millimeter-scale single crystals with well-defined crystallographic orientations. Atomic-resolution STEM observations of these lamellae revealed irreversible local structural changes induced by the delithiation of Li2MnO3 and LiCoO2. In addition, in situ observations enabled direct visualization of the sequential evolution of the domain structure in MoS2 during lithiation.