Synthesis and electrochemical properties of xLiMn_0.9Fe_0.1PO₄·yLi₃V₂(PO₄)₃/C composite cathode materials for lithium–ion batteries

Highlights: • xLiMn_0.9Fe_0.1PO4·yLi₃V₂(PO₄)₃/C composites are prepared by a solid-state method. • The addition of Li₃V₂(PO₄)₃ can improve the properties of LiMn_0.9Fe_0.1PO₄. • Mutual doping occurrs between the LiMn_0.9Fe_0.1PO₄ and Li₃V₂(PO₄)₃ phases. • 5LiMn_0.9Fe_0.1PO₄·Li₃V₂(PO₄)₃/C shows the best electrochemical properties. - Abstract: The xLiMn_0.9Fe_0.1PO₄·yLi₃V₂(PO₄)₃/C (x:y=1:0, 9:1 5:1, 3:1, 1:1 and 0:1) cathode materials are synthesized by a ball–milling and post–calcination method. XRD results reveal that the xLiMn_0.9Fe_0.1PO₄·yLi₃V₂(PO₄)₃/C (x,y≠0) composites are composed of LiMn_0.9Fe_0.1PO₄ and Li₃V₂(PO₄)₃ phases, and no impurities are detected. In LiMn_0.9Fe_0.1PO₄–Li₃V₂(PO₄)₃ system, most of the manganese, iron and vanadium elements in the raw materials tend to form the two major phases, and only small amounts of V, Mn and Fe as dopants enter into the lattice of LiMn_0.9Fe_0.1PO₄ and Li₃V₂(PO₄)₃. Electrochemical tests show that the xLiMn_0.9Fe_0.1PO₄·yLi₃V₂(PO₄)₃/C (x,y≠0) composites exhibit much better performance than the single LiMn_0.9Fe_0.1PO₄/C. Among the samples, 5LiMn_0.9Fe_0.1PO₄·Li₃V₂(PO₄)₃/C shows the best electrochemical performance. The sample delivers the specific capacities of 158.1, 140.7 and 100.2 mAh g⁻¹ at 0.05, 1 and 4 C rates in the potential range of 2.5–4.5 V, and exhibits very long and flat discharge plateau around 4.0 V up to 1 C rate. The sample also shows good cycling performance at various C–rates