B-Mg co-doping behavior of LiFePO4 cathode material: balance of oxygen vacancy and enhancement of electrochemical performance

Increasing the intrinsic conductivity of LiFePO4 can improve its electrochemical performance. Solving this problem can be achieved by P-site doping of LiFePO4 powder. Here, B-Mg co-doped LiFePO4 is successfully synthesized by solvothermal methods. The physical and electrochemical properties of all samples are systematically characterized with various characterization methods. In particular, proper B ion doping is determined to be beneficial to electronic conductivity, which induces the rearrangement of the PO43+ electron cloud. Also, doping with Mg can balance the problems of oxygen vacancies caused by doping B, thereby smoothing the transmission path of lithium ions, resulting in enhanced electrochemical performance. Moreover, XRD and SEM results illustrated that co-doping B and Mg do not change the LiFePO4 structure but promote the formation of a uniform and small particle. Compared with other samples, LiFeMg0.02P0.98B0.02O4 demonstrates superior electrochemical performance, which showed a specific discharge capacity of 147.4 mAh g(-1) at 1 C and a corresponding capacity retention rate of 98.6% after 100 cycles. Even at 10 C, the discharge capacity still maintains 114.9 mAh g(-1). The results of this work indicate that enhancing electronic conductivity and balancing oxygen vacancy are attributed to high electrochemical performance.