Cycling stability of Li₃V₂ (PO₄)₃/C cathode in a broad electrochemical window

In this paper, Li₃V₂(PO₄)₃/C was synthesized using the carbon thermal reduction method. The electrochemical performance of Li₃V₂(PO₄)₃/C in a broad electrochemical window was studied. The fine structure of Li₃V₂(PO₄)₃/C after cycling in different charge and discharge ranges was investigated by X-ray powder diffraction (XRD) refinement, X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results show that the cycling stability of this material decreases with the increase of charge cut-off voltages. After cycling, the unit cell volume of Li₃V₂(PO₄)₃/C expanded irreversibly, in which the lengths of the Li(3)-O and V-O bonds became longer while those of Li(2)-O and Li(1)-O bonds became shorter. In the meantime, the amount of V^{5 +} in the material increased and the carbon layer coated on the surface of the material was destroyed as the charge cut-off voltage was increased from 4.3 to 4.8 V. It is therefore reasonable to infer that the changes in the crystal structure of Li₃V₂(PO₄)₃/C cause the poor cycling performance of Li₃V₂(PO₄)₃/C. This result provides a research idea for improving the cyclic performance of Li₃V₂(PO₄)₃/C in the future.