Effect of sintering time on the synthesize of the multi-layered core–shell LiVOPO4–Li3V2(PO4)3 composite for Li-ion batteries

Abstract

A novel multi-layered core–shell LiVOPO4–Li3V2(PO4)3 composite is synthesized and used as the cathode of lithium ion battery in this work. Composites with different compositions can be obtained by calcining Li3V2(PO4)3 at 350°C for different time in air atmosphere. XRD, SEM, TEM and electrochemical methods are employed to investigate the effect of sintering time on the structure and properties of the prepared LiVOPO4–Li3V2(PO4)3 cathodes. Results indicate that the obtained composites were comprised of a triclinic LiVOPO4 (LVOP) as well as a monoclinic Li3V2(PO4)3 (LVP), and the weight ratio of LVOP increases as prolonging the sintering time based on the Rietveld refinement results. A complete particle in the composite sintered with 2h in air was composed of a core LVP, a shell LVOP as well as some amorphous carbon observed by TEM images, and results from XPS also indicate that the valence of element V was changed from +4 (the shell) to +3 (the core) in the particles. The LiVOPO4–Li3V2(PO4)3 composite synthesized at 2h in air shows the best electrochemical performance with a discharge capacity of 132.8mAhg−1 at 45mAg−1, and the capacity was 126.8mAhg−1 after 100cycles.