Synthesis, characterization and electrochemical performance of Li 2FeSiO 4/C cathode materials doped by vanadium at Fe/Si sites for lithium ion batteries

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 0.9V 0.1O 4/C sample exhibits the best electrochemical performance with initial discharge capacity of 159 mAh g -1 and excellent cyclability with capacity of 145 mAh g -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 0.9V 0.1SiO 4/C sample is only 90% of the undoped Li 2FeSiO 4, which can be attributed to the loss of Fe content. © 2012 Elsevier B.V. All rights reserved.