Supervalent doping of LiFePO 4  for enhanced electrochemical performance

N. V. Kosova; O. A. Podgornova

doi:10.15826/chimtech.2015.2.4.030

Supervalent doping of LiFePO₄ for enhanced electrochemical performance

N. V. Kosova, O. A. Podgornova

Abstract

The orthophosphates LiFe_0.9M_0.1PO₄ with the structure of olivine doped with vanadium and titanium were obtained by mechanochemically stimulated solidphase synthesis using high-energy planetary mill AGO-2 and subsequent annealing at 750 °C. It is shown that V- and Ti- ions do not completely substitute for Fe²⁺ ions in the LiFePO₄ structure. The remaining part of these ions involve in the formation of second phase with nashiko-like structure: monoclinic Li₃V₂(PO₄)₃ (space group P2₁/n ) and rhombohedral LiTi₂(PO₄)₃ (space group R-3c). According to TEM, the average size of the particle of nanocomposites is about 100-300 nm. EMF of microanalysis showed that the small particles of secondary phases are segregated at the surface of larger particles of LiFePO₄. On the charge-discharge curves of LiFe_0.9M_0.1PO₄ there are plateau corresponding to LiFePO₄ and the second phase. The doping with vanadium increases the resistance of the cycling of LiFePO₄ and improves its cyclability at high speeds to a greater extent than in the case of doping with titanium.

Keywords

LiFePO4; supervalence doping; mechanochemical activation; electrochemical cycling

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DOI: https://doi.org/10.15826/chimtech.2015.2.4.030

Copyright (c) 2015 N. V. Kosova, O. A. Podgornova