Investigation of phase structure change and electrochemical performance in LiVP2O7-Li3V2(PO4)3-LiVPO4F system

Vanadium phosphates have attracted considerable attention in Li-ion battery research because they feature the chemical activity of vanadium and the structural stability of phosphate. Novel LiVP2O7-Li3V2(PO4)3-LiVPO4F systems were synthesized through solid-state reaction, and the chemical reaction, phase formation, and phase structure change of LiVP2O7, Li3V2(PO4)3, LiVPO4F were investigated using TG-DTA, XRD, and TEM tests. Results indicate that Li3V2(PO4)3, LiVP2O7, and LiVPO4F coexist in samples sintered at 575 °C, and the three phases transform into one other by changing the sintering temperature. Electrochemical tests show that different electrochemical performances can be obtained by regulating the contents of each phase (LiVP2O7, Li3V2(PO4)3, or LiVPO4F). The LiVP2O7-Li3V2(PO4)3 sample synthesized at 625 °C shows much better electrochemical performance because of the synergistic effects between Li3V2(PO4)3 and LiVP2O7.