Rheological phase synthesis and characterization of Li3V2(PO4)3/C composites as cathode materials for lithium ion batteries

Li3V2(PO4)3/C composites as cathode materials for lithium ion batteries were successfully synthesized through the rheological phase reaction method using LiOH·H2O, V2O5, NH4H2PO4, and C6H8O7·H2O as raw materials. The as-prepared powders were characterized by means of powder X-ray diffraction (XRD), scan electron microscope (SEM), and transmission electron microscope (TEM). The electrochemical properties of Li3V2(PO4)3/C composites were examined by the galvanostatic charge/discharge, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results indicate that the sintering temperatures have a significant effect on the crystal structure, morphology, and electrochemical performances of Li3V2(PO4)3/C composites. XRD reveals that Li3V2(PO4)3/C composites are well crystallized single phase, where Li3V2(PO4)3/C composite synthesized at 800 °C for 8 h displays the maximum cell volume and uniformly distributed particles. It can be seen from TEM that there is a carbon layer of about 200-500 nm thick on the particle surface. The apparent DLi+ calculated from CV is in the order of magnitude of 10−7 cm2 s−1. Electrochemical tests show that Li3V2(PO4)3/C composite synthesized at 800 °C for 8 h exhibits excellent cycling performance of 129.149 mAh g−1 after 60 cycles at the current of 15 mA g−1 and a superior rate capability of 112.101 mAh g−1 after 60 cycles at the current of 90 mA g−1.