Synthesis, characterization and electrochemical performance of Li2FeSiO4/C cathode materials doped by vanadium at Fe/Si sites for lithium ion batteries

摘要

Li_2FeSiO_4/C composites doped by vanadium at Fe/Si sites have been investigated as cathode materials for lithium ion batteries. Effects of vanadium substitution at different sites on the structure of Li_2FeSiO_4/C are examined by X-ray diffraction, X-photoelectron spectroscopy and scanning electron microscopy. XPS results show that the oxidation state of vanadium doped at Fe sites is +3, whereas is +5 when doped at Si sites. Electrochemical measurements show that the Li_2FeSi_(0.9)V_(0.1O4)/C sample exhibits the best electrochemical performance with initial discharge capacity of 159mAhg~(-1) and excellent cyclability with capacity of 145mAhg~(-1) at 30th cycle, which can be ascribed to larger cell volume and higher lithium ion diffusion coefficient, however, the initial discharge of the Li_2Fe_(0.9)V_(0.1)SiO_4/C sample is only 90% of the undoped Li_2FeSiO_4, which can be attributed to the loss of Fe content.