Evolution of electrochemical performance in Li3V2(PO4)3/C composites caused by cation incorporation

Li3V2(PO4)(3)/C (LVP/C) composites incorporated by a series of electrochemically active cations (Fe, Co, Ni, Mn) have been successfully prepared by a conventional solid-state reaction. M-incorporation (M = Fe, Co, Ni, Mn) in Li3V2(PO4)(3)/C does not change the monoclinic structure. Analyzed with X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and high-resolution transmission electron microscopy, we find that the valence is between +2.67 and +3 for Fe, and is +2 for Co, Ni and Mn. M-doped LVP and LiMPO4 phases coexist in the incorporated LVP/C composites. Compared with pristine LVP/C, Feincorporated LVP/C shows the best electrochemical performance with the highest initial discharge capacity of 131.4 mAhg(-1) at 0.1C between 2.5 and 4.3 V. The Fe-incorporated LVP/C sample also exhibits excellent rate capability with an average capacity of 122.4 mAh g(-1) at 1C and 93.5 mAhg(-1) at 5C, resulting from the reduced particle size, the improved electronic conductivity, the high Li-ion diffusion coefficient, and the contribution of LiFePO4 to the capacity. (C) 2013 Elsevier Ltd. All rights reserved.