Synthesis and electrochemical performance of Li3NbO4-based cation-disordered rock-salt cathode materials for Li-ion batteries

摘要

In this reported study, Li3NbO4-based, Li-excess cathode materials xLi(3)NbO(4)center dot(1-x) LiMnO2 (0.2 < x < 0.5) were synthesized using a solid state reaction method. XRD results showed that the fabricated powders with x = 0.3-0.5 could be indexed to a typical rock-salt structure (Fm-3m space group). Rietveld refinements showed that the lattice parameters increased with the increase in Nb5+ content. SEM and TEM images of the product showed that the elements Nb, Mn and O were evenly distributed in the samples, which further confirmed the cubic rock-salt structure of the product. Electrochemical tests of the samples showed that the sample with x = 0.4 exhibited the best electrochemical performance (232 mAh/g in the first cycle and more than 175 mAh/g in 50 cycles, as well as relatively high discharge capacity at high discharge current density). The redox mechanism analysis of the experimental results indicated that there were two stages in charge process: one was the Mn3+/4+ oxidation reaction below 4.3 V, and the other was related to the oxidation of O2- to O- or the release of O-2, which improved the reversible capacity of the material. The structural evolution analysis of the samples showed that a spinel phase structure was present during the cycling process and the shift in the XRD peaks indicated that the sample with x = 0.4 exhibited the best structural stability. The electrochemical impedance spectroscopy analysis showed that the sample with x = 0.4 had the smallest R-ct. The results for the kinetics of lithium ion diffusion indicated that the sample with x = 0.4 had largest D-Li(+), which was consistent with the best electrochemical performance for this material, especially the rate capability. (C) 2019 Elsevier B.V. All rights reserved.