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

• Cation-incorporated Li3V2(PO4)3/C have been systematically investigated.
• Cation incorporation in Li3V2(PO4)3 does not change the monoclinic structure but form solid solution.
• Fe-incorporation shows the best electrochemical performance whereas Ni-incorporation shows the poorest performance.
• A clear profile of cation incorporation with Fe, Co, Ni, Mn ions in Li3V2(PO4)3/C is obtained.

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 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, Fe-incorporated LVP/C shows the best electrochemical performance with the highest initial discharge capacity of 131.4 mAh g−1 at 0.1 C 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 1 C and 93.5 mAh g−1 at 5 C, resulting from the reduced particle size, the improved electronic conductivity, the high Li-ion diffusion coefficient, and the contribution of LiFePO4 to the capacity.

Four electrochemically active cations (M = Fe, Co, Ni, Mn) are doped into Li3V2(PO4)3. M-incorporation does not change the monoclinic structure of Li3V2(PO4)3, but forms some solid solutions. Minor LiMPO4 impurity phases can be formed in the LVMP/C samples. Moreover, FePO4 also exists as impurity in the LVFeP/C sample. Compared with pristine LVP/C, LVNiP/C electrode exhibits the lowest capacity, resulting from the decreased electronic conductivity and the lowest Li-ion diffusion coefficient, whereas LVFeP/C shows the best electrochemical performance.Figure optionsDownload as PowerPoint slide