Optimized electrochemical performance of LiMn0.9Fe0.1−xMgxPO4/C for lithium ion batteries

A series of LiMn_0.9Fe_0.1−xMg_xPO₄/C (x = 0, 0.01, 0.02, 0.05) was synthesized by a solid state reaction, and the effect of synthesis temperature and Fe/Mg ratio on the electrochemical performance of the obtained materials was investigated by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and electrochemical measurements. The electrochemical performance of the Fe and Mg co-substituted LiMnPO₄ was obviously improved with increasing synthesis temperature from 650 to 800 °C, but further increase led to an abrupt capacity loss due to the impurity formation. The Fe and Mg co-substitution could remarkably enhance the electrochemical activity of LiMnPO₄ compared with the Fe substitution only, but too high level of Mg doping would worsen the rate capability. The LiMn_0.9Fe_0.09Mg_0.01PO₄/C synthesized at 800 °C demonstrated the optimum electrochemical performance with a high capacity and an excellent rate capability. Even discharged at the rate of 10 C, a capacity of 60 mAh g⁻¹ was still observed.