Influence Mechanism of Mg2+ Doping on Electrochemical Properties of LiFePO4 Cathode Materials

For this work, a Mg2+-doped LiFePO4 (LFP) cathode material was prepared using a solid-state method with Mg(CH3COO)2 as the Mg2+ dopant. X-ray diffraction and refinement data suggested that an appropriate doping amount of Mg2+ can reduce the cell volume of LFP, shorten the Fe–O and P–O bonds, and elongate the Li–O bond, thereby facilitating the diffusion of Li+. X-ray photoelectron spectroscopy test results revealed that Mg2+ doping prevents the formation of Li–Fe antisite defects while also promoting the formation of Fe2P, thereby improving the electronic conductivity of the LFP. The electronic conductivity was measured using a four-probe teste, and the Li+ diffusion rate was fitted and calculated according to the electrochemical impedance spectroscopy test results. The results found that electron conductivity expanded by 275 times and the Li+ diffusion coefficient increased by 3.6 times following LFP being doped with Mg2+. Charge/discharge curves and cyclic voltammetry test reveal that LFP with Mg2+ doping has superior reversibility, rate performance, and cycle stability, and the capacity can be maintained at 162 mA h g–1 following 300 cycles at 0.1 C.