The device developed here for XRD analysis is built on a Guinier-Lenne geometry camera. A monochromatized and focused beam goes through the plastic Li-ion cell protected by a metal-plastic laminate. Each layer of the cell gives diffracted beams, which are collected on an X-ray film on the focus circle. The film is continuously moved up (1-2 mm/h), while the Li-ion cell is charged and discharged, and controlled by means of the Mac-pile system. Both plastic electrodes crystallographic behavior can be simultaneously and continuously observed under the real operating conditions of a commercial battery. Comparison between C/LixNiO2 and C/LixNi0.7Co0.3O2 batteries is given as an example. Parameters evolution of the two electrodes can easily be correlated with the cycling curves. Studies can also be performed from room temperature up to 100 degrees C.