No P3-type phase of NaxMO2 with x close to unity

Abstract

Layered AxMO2 phases attract great attention as electrode materials for high-energy density batteries. The main structural variants in this family are know n as O3, P2 and P3. Previous experimental data and theoretical considerations have shown that prismatic structures with A = Na or K can only be stable at x values significantly lower than unity, typically 0.6–0.8 for P2 and 0.5–06 for P3 (if any). This was challenged by recent reports on P3-type Na0.9(Fe0.5Mn0.5)O2 and Na(Cu0.2Fe0.1Mn0.7)O2. We found, however, that the reported XRD patterns strongly disagree with the reported structures and compositions. For the former, actual lattice parameters correspond to an x value much lower than 0.9, and the latter is actually P2 type with x close to 0.74.