Abstract: To develop an effective battery cathode material that can be useful for future batteries, the thermal stability and ion migration dynamics need to be well understood. In situ transmission electron microscopy (TEM) is a popular and proven technique to study the evolution of local structures during the dynamic processes in the cathode materials. This dissertation will demonstrate the application of high-resolution imaging and in situ heating and biasing in the TEM to study the structure and composition, morphology change, and ion migration in the cathode materials.   The three chapters in this dissertation will be focused on the two cathode materials: zeta (?) vanadium pentoxide, and chromium intercalated sodium manganese oxide. The first project demonstrates the effect of in situ heating method, nanowire size, sodium content, and vacuum condition on the thermal stability of zeta (?) vanadium pentoxide in real-time in the TEM. The second project concentrates on in situ biasing in the TEM to study the sodium ion migration, silver exsolution, and negative differential resistance phenomenon in the zeta (?) vanadium pentoxide. The third project concentrates on the synthesis and characterization of chromium incorporated sodium manganese oxide. The works presented here show the capability of in situ TEM imaging techniques to study the dynamic changes in the structure and composition of the nanomaterials during the heating and biasing processes.