The doping effect on the crystal structure and electrochemical properties of LiMnxM1−xPO4 (M = Mg, V, Fe, Co, Gd)

Abstract To substitute minor Mn 2+ by the transition metal ion M = Mg 2+ , V 3+ , Fe 2+ , Co 2+ , or Gd 3+ , LiMn 0.95 M 0.05 PO 4 samples are synthesized by a solid-state reaction route. The interpretation of doping effects is complicated by the interrelations between doping microstructure and morphology, because the crystal structure would be affected by the doped elements. The lattice structure and deviation of Li–O bond lengths of the doped LiMnPO 4 are refined by XRD refinement. All the samples present a couple of oxidation and reduction peaks in cyclic voltammetry, corresponding to a redox Mn 3+ /Mn 2+ reaction coupled with the extraction/reinsertion process of Li + in LiMnPO 4 structure. During charge/discharge process, the electron flowing and Li + cation diffusion in the various doped LiMnPO 4 samples should be different thermodynamic and kinetic process. For further studying which step in thermodynamic and kinetic process would affect or control the electrochemical performance, the initial charge/discharge capacities and cycleability of doped LiMnPO 4 samples are obtained under different voltage range (from 2.7 to the upper cut-off voltage 4.4, 4.6 and 4.8 V, respectively) and different environment temperatures (0, 25, and 50 °C). At relative higher measuring temperature, the discharge capacity of Co-doped LiMnPO 4 shows 151.9 mAh g −1 .