For energy-related materials, the understanding of property-structure relationship is based on the knowledge of their structure, interfaces and phase evolution. Advanced (scanning) transmission electron microscopy ((S)TEM) techniques have been applied to investigate the structure as well as their functions of the energy-related materials, with the help of combined electrochemical and theoretical approaches. In the first part of this talk, I will discuss my recent work on TEM characterization of the conversion oxide compounds for lithium/sodium ion batteries. While our ex situ TEM study reveal the structural change in the real cell probe local structural and chemical information at a spatial resolution of nanoscale., in situ TEM study can help us to understand the process of lithiation/sodiation. In the cases of rocksalt-structure oxide (NiO) and spinel oxides (Fe3O4 and Co3O4) compounds, we have investigated the dynamical process of the redox reaction in real time. The role of reaction pathways is highlighted which is supposed to affect the batteries’ kinetic properties. In the second part of the talk, I will discuss the strain coupling of highly uniform PtPb/Pt core/shell nanoplates, which may help to optimize the Pt-O bond strength and therefore boost their activity and stability for oxygen reduction reaction (ORR).