Structural changes of electrodic materials in electrochemical cells observed by in situ energy dispersive X-ray diffraction (EDXD)

The in situ observation of the structural changes induced in electrodic act ive materials upon cycling is commonly performed by angular dispersive X-ra y diffraction (ADXD). Here an alternative approach based on the energy disp ersive X-ray diffraction (EDXD) is described, together with its application to the study of the well-known LiNi0.8Co0.2O2 cathode material. In the fir st part, we briefly describe the technique and its application to the in si tu study of electrode materials. In the second part, we discuss how the exp erimental data have to be processed in order to separate the signal produce d 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 LiNi0.8Co0.2O 2 during the first three charge-discharge cycles is shown in terms of the l attice parameters time evolution. The results confirm what was already repo rted in the literature on the behavior of similar materials, providing, at the same time, detailed information on the evolving structure. In fact, alt hough the resolution of EDXD is lower than that of ADXD, the measurements h ave a good accuracy, which guarantees a small statistical scattering of the lattice parameters experimental points. This, together with the high sampl ing density, gives the points the aspect of almost continuous curves, whose features can be of interest in the study of electrodic materials.