Effect of impurities in FePO4 raw materials on the performance of LiFePO4 cathode materials

Here, the effects of Mg2+, Mn2+, and SO42- impurities in FePO4 raw materials on the properties of LFP were studied by converting impurities into doping elements. The results indicate that due to differences in ionic radius and doping methods, these three impurities have varying impacts on the performance of LFP. 0.2-0.6% Mg2+ doping can significantly improve the high-rate capacity and cycle performance of LFP materials. At 5 C, the discharge specific capacity reaches 122.39 mAh/g, respectively, and the discharge specific capacity retention rate is 94.7% after 500 cycles. By contrast, Mn2+ doping leads to a significant decline in the rate performance of LFP. SO42- is decomposed and reduced during synthesis, which slightly reduces the electrochemical performance of LFP. Therefore, it is not the case that a higher purity of FePO4 yields better results. An appropriate amount of Mg2+ should be retained, SO42- should be controlled at a low level, and Mn2+ should be minimized. Different impurities should be treated differently to reduce the preparation cost of the raw material.