Electrochemical Performance of Li0.995Al0.005Mn0.85Fe0.15PO4/C as a Cathode Material for Lithium-Ion Batteries

A solid-state reaction route was used to prepare Li0.995Al0.005Mn0.85Fe0.15PO4/C, and the prepared sample were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and electrochemical tests. The results of XRD and XPS show that Al3+ and Fe2+ are soluble in the Li site and the Mn site to generate a solid-solution, resulting in a shrinkage of crystal lattice and creations of Al3+ -vacancy pairs and Fe3+-vacancy pairs. Compared with Li0.995Al0.(005) MnPO4/C, LiMn0.85Fe0.15PO4/C, Li0.995Al0.005Mn0.85Fe0.15PO4/C exhibits much better rate capability and cycling stability. When charged and discharged at 1 C, Li0.995Al0.005Mn0.85Fe0.15PO4/C delivers a discharge capacity of 139 and 160 mAh g(-1) at 25 and 60 degrees C, and its capacity retention ratio is 100 % after 50 cycles, respectively. The enhanced property of LiMnPO4/C can be attributed to the synergistic effect of Al3+ doping at the Li site and Fe2+ doping at the Mn site, leading to a great improvement in the dynamic stability of the olivine structure, Li+ diffusion and electrode kinetics. Thus, the electrochemical properties of lithium manganese phosphate can be effectively improved by Fe2+ doping at the Mn site and aliovalent ion doping at the Li site.