The doping modification of PO43− or BO33− on the electrochemical performance of Li2Fe0.98Mg0.02SiO4/C cathode materials

Abstract

In this paper, the solid-phase method is adopted in the synthesis of Li2Fe0.98Mg0.02(SiO4)1−x(PO4)x/C and Li2Fe0.98Mg0.02(SiO4)1−x(BO3)x/C (x = 0.01, 0.02, 0.03, 0.05). The Li2Fe0.98Mg0.02(SiO4)0.97(PO4)0.03/C has an initial discharge capacity of 170.4 mAh/g. The initial discharge capacity of Li2Fe0.98Mg0.02(SiO4)0.95(PO4)0.05/C is 152 mAh/g. After PO43− is doped at the Si site, a peak appears at 3.1 V in the oxidation curve of the CV graph, indicating that more Li+ participate in the electrochemical reactions, which finally increases the peak area and the capacity of the modified material. The initial discharge capacity of Li2Fe0.98Mg0.02(SiO4)0.97(BO3)0.03/C is 138 mAh/g. The SEM shows the particle sizes of those two materials are uniform. According to the XRD, there is a weak characteristic peak of Li2Fe3O4 impurity found in the Li2Fe0.98Mg0.02(SiO4)0.97(BO3)0.03/C, while no characteristic peak of impurity is found in the Li2Fe0.98Mg0.02(SiO4)0.95(PO4)0.05/C, and its cell volume increases slightly which is beneficial to improve the electrochemical performance of the material.