Effects of Ti and Mg Codoping on the Electrochemical Performance of Li3V2(PO4)3 Cathode Material for Lithium Ion Batteries

Ti and Mg codoped Li 3 V 2–2 x Ti x Mg x (PO 4 ) 3 ( x = 0, 0.05, 0.10, 0.20, and 0.25) samples were prepared by a sol–gel method. The effects of Ti and Mg codoping on the physical and electrochemical characteristics of Li 3 V 2 (PO 4 ) 3 were investigated. Compared with the XRD pattern of the undoped sample, those of the Ti and Mg codoped samples have no extra reflections, which indicates that Ti and Mg enter the structure of Li 3 V 2 (PO 4 ) 3 . According to the results of charge–discharge measurements, the initial capacity of Li 3 V 2–2 x Ti x Mg x (PO 4 ) 3 at a low current density (0.2 C) decreases with increasing x . However, the discharge capacities at higher current densities (1 and 2 C) and the cycling stability are improved by a low amount of Ti and Mg codoping ( x = 0.05), and moreover, EIS measurements indicate the lower charge transfer resistance of Li 3 V 1.9 Ti 0.05 Mg 0.05 (PO 4 ) 3 . The improved electrochemical performance of Li 3 V 1.9 Ti 0.05 Mg 0.05 (PO 4 ) 3 can be attributed to its higher structural stability and smaller particle size. When x is higher than 0.05, the charge transfer resistance increases with increasing x, which leads to their poor electrochemical performance.