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The in situ observation of the structural changes induced in electrodic active materials upon cycling is commonly performed by angular dispersive X-ray diffraction (ADXD). Here an alternative approach based on the energy dispersive X-ray diffraction (EDXD) is described, together with its application to the study of the well-known LiNi0.8Co0.2O2 cathode material. In the first part, we briefly describe the technique and its application to the in situ study of electrode materials. In the second part, we discuss how the experimental data have to be processed in order to separate the signal produced by the active material only from that of the other parts of the cell. In the third part, a dense sampling of the changing structure of LiNi0.8Co0.2O2 during the first three charge−discharge cycles is shown in terms of the lattice parameters time evolution. The results confirm what was already reported in the literature on the behavior of similar materials, providing, at the same time, detailed information on the evolving structure. In fact, although the resolution of EDXD is lower than that of ADXD, the measurements have a good accuracy, which guarantees a small statistical scattering of the lattice parameters experimental points. This, together with the high sampling density, gives the points the aspect of almost continuous curves, whose features can be of interest in the study of electrodic materials.