Electrochemical performance of LiFe1−xVxPO4/carbon composites prepared by solid-state reaction

LiFe1−xVxPO4/C cathode materials (x = 0, 0.1, 02, 0.3, 0.4) were synthesized by solid-state reaction using polypropylene as the reducing agent and carbon precursor. XRD results show that Li9Fe3P8O29 and Li3V2(PO4)3 occur when vanadium was added. TEM images show that most of LiFe1−xVxPO4/C particles take on a spherical or quadrate shape with a size less than 200 nm. Electrochemical tests indicate that LiFe0.9V0.1PO4/C and LiFe0.8V0.2PO4/C have a flat discharge plateau at about 3.45 V versus Li+/Li and an initial discharge capacity higher than 150 mAh/g at 0.1 C. LiFe0.8V0.2PO4/C also performed relatively good cycle stability which is attributed to their high electronic conductivity as proved by the electrochemical impedance spectroscopy (EIS). Cyclic voltammogram (CV) curves demonstrate that as increase of content of vanadium, LiFe1−xVxPO4/C presents several couples of redox peaks.