V2O3 modified LiFePO4/C composite with improved electrochemical performance

In addition to lattice doping and carbon-coating, surface modification with other metal oxides can also improve the electrochemical performance of LiFePO4 powders. In this work, highly conductive vanadium oxide (V2O3) is in situ produced during the synthesis of carbon-coated LiFePO4 (LiFePO4/C) powders by a solid state reaction process and acts as a surface modifier. The structures and compositions of LiFePO4/C samples containing 0–10 mol% vanadium are analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. Their electrochemical properties are also characterized with galvanostatic cell cycling and cyclic voltammetry. It is found that vanadium is present in the form of V2O3 that is incorporated in the carbon phase. The vanadium-modified LiFePO4/C samples show improved rate capability and low-temperature performance. Their apparent lithium diffusion coefficient is in the range of 10−12 to 10−10 cm2 s−1 depending on the vanadium content. Among the investigated samples, the one with 5 mol% vanadium exhibits the best electrochemical performance.

► Introduction of a small amount of vanadium into the carbon-coated LiFePO4 particles leads to significant improvement in the rate capability and low-temperature performance.
► The modification mechanism is directly related to the formation of conductive V2O3 nano-grains.
► V2O3 increases the degree of graphitization of the carbon layer so that the composite conductivity is increased.