Advanced (scanning) transmission electron microscopy ((S)TEM) has been applied to study the redox reactions of the electrode materials for secondary ion batteries. With/Combining different TEM techniques (including in situ TEM and diffraction, HAADF-STEM, and STEM-electron energy-loss spectroscopy (EELS)), researchers are able to probe local structural and chemical information of electrode materials, at a resolution of nanoscale. Knowledge about the reaction dynamics and kinetics can be retrieved at different states of charging (discharging). This talk will cover the recent progress on TEM characterization of the conversion compounds for lithium/sodium ion batteries. While the ex situ TEM study reveal the structural change in the real cell, 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 for electrode materials, we 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. Our results may give insights in developing new electrode materials for high performance batteries.