Effects of Mn2+ doping on structure, performance and kinetic of lithium-ion insertion of LiFePO4 positive-electrode material

Abstract:

To improve the performance of olivine LiFePO₄ positive-electrode material, the Mn-doped LiMn_xFe1-xPO₄(x=0,0.0,0.5,0.0,0.50) materials were prepared by a solid-state reaction method. The structure, electrochemical performance and lithium ion insertion-extraction kinetic of the material are investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD), charge-discharge tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that the Mn-doped LiFePO₄ material powders have a uniform morphology, a small particle size and narrow particle size distribution, and LiMn_xFe1-xPO₄ materials are pure phase olivine structure. LiMn0.4Fe0.6PO₄ shows the highest discharge capacity and the best kinetic performance among all samples at different rates. The Mn doping improves the reversibility, Li+ions diffusion coefficient and discharge capacity, and reduces the charge transfer resistance, and then increase the kinetic performance of LiFePO₄ material.