Enhancement of the cycling performance of Li3V2(PO4)3/C by stabilizing the crystal structure through Zn²âº doping.

ABSTRACT

A series of Li3V(2-2/3x)Zn(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(2-2/3x)Zn(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.