The variations of structure and microstructure of electrode materials in a graphite/LiCoO₂ battery during charge-discharge process have been studied by X-ray diffraction (XRD). It is revealed that, in the charge process, as intercalating into 2H-graphite, Li atoms preferentially occupy interstitial sites between C atom hexagonal net planes, which leads to increase of the lattice parameter a, c and micro-strain ε and change of stacking disorder P of 2H-graphite. When the battery is 20% charged, Li-C compounds are formed in the anode. Meanwhile, as for the cathode, in the charge process Li atoms occupying (000) sites may preferentially de-intercalate from LiCoO₂ crystal lattice. With increase of the amount of Li de-intercalating, the lattice parameter, a and c, decreases and increases respectively, and its micro-strain ε increases. During the whole process of charge and discharge, no phase transformation happens to LiCoO₂. Finally, the conductive mechanism of Li-ion battery has been discussed. The main points are as follows: the transference of Li-ion starts from the anode-electrolyte interface in the charge process and reversely from the cathode-electrolyte interface in the discharge process. The intercalation and de-intercalation of Li into and from cathode and anode all go through a process from the surface to the inside of the particles. The charge and discharge processes of Li-ion battery are not fully reversible.

Key words: Li-ion battery, microstructure, X-ray diffraction, conductive mechanism