Reversible intercalation of lithium in a host material results in an electron donation from the alkali metal to the guest compound. This reduction generally takes place on the transition metal, which is the species presenting accepting (i.e. empty or partially filled) d levels. When starting from a high oxidation state for that cation, the intercalates seem to be rather stable and no atomic structure change of the host is observed. An important exception arises with molybdenum disulphide. This particular case corresponds to a prismatic cation environment, whose stability decreases with reduction of Mo 4+ into Mo 3+. When the transition metal oxidation state is rather low, instability of its new electronic configuration acquired upon reduction may lead also to its shift to more stable coordination. This is encountered for the thiophosphate NiPS 3, in which reduced nickel atoms migrate from an octahedral to a tetrahedral environment. The cationic coordination change of the two examples takes place from the very beginning of the intercalation process. A transition metal displacement may also take place in order to balance the ionic charge distribution which was distributed by the reduction (or oxidation) reaction. This is a way for the crystal network to maintain the highest coulombic energy, the host cations remaining in the same coordination. Examples of this behaviour are given by the A xMO 2 (A = Na, Li) ternary oxides and the Li xFeS 2 system. The other difference between this cationic shift and the previous ones lies in the fact that this latter phenomenon is not a progressive one: it does not take place in the early stage of the intercalation-deintercalation process. Actually, it happens at a given intercalation rate, as if there was a threshold value for the shift to happen. Some of the transition metal shifts studied are only partially reversible, with some of the reoxidized cations remaining in their new surroundings. This may account for the forming (and/or aging) of cathodic materials, whereas the massive movement of these ions during the redox reaction may explain the progressive amorphization of the positive materials and account for their new electrochemical behaviour.