The role of aberration-corrected scanning transmission electron microscopy (STEM) in materials characterization is examined with respect to layered-oxide cathode materials for battery applications. STEM-based methods are quickly becoming the most promising characterization tools for these materials, owed largely to the wide-range of techniques available on advanced STEM instruments, including the direct imaging of both heavy and light elements, and both energy-dispersive X-ray (EDX) and electron energy loss (EEL) spectroscopies. The current talk will focus on multiple Li-based, Mn-containing oxide cathode materials, for example, Li₂MnO₃ and Li(Ni_0.5Co_0.2Mn_0.3)O₂), characterized via STEM methods, in pristine, cycled, and in-situ irradiated states. The latter allows for single particle tracking of the dynamic processes occuring upon Li and O loss from the material, and is a form of accelerated ageing compared to the structural and electronic changes which occur upon electrochemical cycling. Various imaging modes, including high/low angle annular dark field (H/LAADF) and annular bright field (ABF), in conjunction with EELS/EDX, will be used extensively for this analysis, while parameters such as Mn valence, O presence, and light element occupation and intercalation will be discussed.