Layered oxides are the subject of intense studies either for their properties as electrode materials for high-energy
batteries or for their original physical properties due to the strong electronic correlations resulting from their unique
structure. Here we present the detailed phase diagram of the layered P2-NaxVO2 system determined from electrochemical intercalation/deintercalation in sodium batteries and in situ X-ray diffraction experiments. It shows that four main single-phase domains exist within the 0.5<x<0.9 range. During the sodium deintercalation (intercalation), they differ from one another in the sodium/vacancy ordering between the VO2 slabs, which leads to commensurable or incommensurable superstructures. The electrochemical curve reveals that three peculiar compositions exhibit special structures for :xD1=2, 5/8 and 2/3. The detailed structural characterization of the P2-Na1=2VO2 phase shows that the NaC ions are perfectly ordered to minimize NaC/NaC electrostatic repulsions.Within the VO2 layers, the vanadium ions form pseudo-trimers with very short V–V distances (two at 2.581Å and one at 2.687Å). This original distribution leads to a peculiar magnetic behaviour with a low magnetic susceptibility and an unexpected low Curie constant. This phase also presents a first-order structural transition above room temperature accompanied by magnetic and electronic transitions. This work opens up a new research domain in the field of strongly electron-correlated materials. From the electrochemical point of view this system may be at the origin of an entire material family optimized by cationic substitution
