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

To substitute minor Mn2+ by the transition metal ion M = Mg2+, V3+, Fe2+, Co2+, or Gd3+, LiMn0.95M0.05PO4 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 LiMnPO4 are refined by XRD refinement. All the samples present a couple of oxidation and reduction peaks in cyclic voltammetry, corresponding to a redox Mn3+/Mn2+ reaction coupled with the extraction/reinsertion process of Li+ in LiMnPO4 structure. During charge/discharge process, the electron flowing and Li+ cation diffusion in the various doped LiMnPO4 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 LiMnPO4 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 degrees C). At relative higher measuring temperature, the discharge capacity of Co-doped LiMnPO4 shows 151.9 mAh g(-1). (C) 2011 Elsevier B.V. All rights reserved.