Transmission electron microscopy (TEM) is a powerful tool which we are applying to study the microstructure of carbonaceous materials that are used as lithium-intercalation electrodes in lithium-ion cells. The results of our study on the relationship between the physicochemical properties of carbon, with strong emphasis on the microstructure observed by TEM, and their capability for electrochemical intercalation of lithium will be summarized. In addition, progress on the fabrication of a microcell for in situ TEM of lithium-intercalation in carbon will be discussed.