Synthesis, crystal structure and electrochemical properties of the manganese-doped LiNaFe[PO4]F materials

The new compounds LiNaFe1−xMnx[PO4]F (x ≤ 1/4) were synthesized by a solid state reaction route. The crystal structure of LiNaFe3/4Mn1/4[PO4]F was determined from single crystal X-ray diffraction data. LiNaFe3/4Mn1/4[PO4]F crystallizes with the Li2Ni[PO4]F-type structure, space group Pnma, a = 10.9719(13), b = 6.3528(7), c = 11.4532(13) Å, V = 798.31(16) Å3, and Z = 8. The structure consists of edge-sharing (Fe3/4Mn1/4)O4F2 octahedra forming (Fe3/4Mn1/4)FO3 chains running along the b-axis. These chains are interlinked by PO4 tetrahedra forming a three-dimensional framework with the tunnels and the cavities filled by the well-ordered sodium and lithium atoms, respectively. The manganese-doped phases show poor electrochemical behavior comparing to the iron pure phase LiNaFe[PO4]F.