Enhancement of discharge capacity of Li3V2(PO4)3 by stabilizing the orthorhombic phase at room temperature

Li3V2(PO4)3 and solid solutions of Li3−2x(V1−xZrx)2(PO4)3 were prepared by a solid state reaction. A high temperature orthorhombic phase of Li3V2(PO4)3 with a β-Fe2(SO4)3-type was successfully stabilized at room temperature by substituting Zr for V with substitution ratios beyond x=0.05. The pure material of Li3V2(PO4)3 exhibited a cathode performance with two well defined regions of plateau at around 3.7 and 4.1 V vs. Li/Li+ upon charging and 3.6 and 4.0 V vs. Li/Li+ upon discharging, respectively, suggesting two types of phases produced upon the charge/discharge process. On the other hand, the cathode performance of the orthorhombic stabilized materials showed almost the same charge/discharge voltages as those of the pure material, but, with two plateaus slightly sloping, showed a considerably improved charge/discharge cycle performance compared to that of the pure material. Such improvement on the charge/discharge cycle performance is suggested to come from the disordered lithium ion arrangement in the orthorhombic phase.