Enhancement of the cycling performance of Li3V2(PO4)3/C by stabilizing the crystal structure through Zn2+ doping

Abstract

A series of Li₃V_2−2/3xZn_x(PO₄)₃/C phases were synthesized by carbon thermal reduction assisted by the ball-mill process. Scanning electron microscopy (SEM) showed that the irregular morphology of the pristine Li₃V₂(PO₄)₃/C could be transformed to spherical upon doping with a suitable amount of zinc. The structural stability of the pristine and the Zn doped Li₃V₂(PO₄)₃/C were investigated via X-ray absorption near edge structure (XANES) spectroscopy and X-ray diffraction (XRD). The results revealed that Zn doping not only improves the stability of the VO₆ octahedral structures before electrochemical cycling, but also reduces the degree of irreversible expansion of the c axis and the crystal volume upon repeated cycles. Among the Li₃V_2−2/3xZn_x(PO₄)₃/C (0 ≤ x ≤ 0.15) series, the sample doped with 0.05 Zn atoms per formula unit showed the best electrochemical performance. Excess Zn doping (x > 0.05) didn't result in further improvement in the electrochemical performance due to the segregation effect and the inactive nature of Zn.