Synthesis, characterization, and electrochemical properties of Li2Mn1-xFex(PO3)4 cathode material for lithium-ion batteries

Li2Mn1-x Fe x (PO3)4 (x = 0, 0.2, 0.4, 0.6, 0.7) solid solution phase has been successfully prepared via solid-state reaction. The Rietveld refinement results indicate that the Li2Mn1-x Fe x (PO3)4 (x = 0, 0.2, 0.4, 0.6, 0.7) solid solutions with orthorhombic structure can be obtained and the lattice parameters (including a, b, c, and V) decrease with the increasing of Fe concentration. Partial substitution of manganese with iron enhances the electrochemical performance; there, the discharge-specific capacity of the samples obviously increases from 21 mAh/g for x = 0 to 59 mAh/g for x = 0.7, which is 85 % capacity of that one lithium removal. The cyclic voltammetric (CV) curves present the Mn2+/Mn3+ redox couple situated at 4.6 and 1.8 V and Fe2+/Fe3+ redox couple located at 4.3 and 2.3 V, which can be observed in cathodic and anodic sweeps. Such a low discharge potential value for M2+/M3+ redox couple may be attributed to the zigzag [(PO3)1−] n chains in this structure.