Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7725371 | Journal of Power Sources | 2018 | 11 Pages |
Abstract
Insertion of 3% vanadium in LiMn1-yFeyPO4 has been investigated, with yâ¯=â¯0.2 corresponding to the highest manganese concentration before the stress/strain field degrades the electrochemical performance. V substitutes for Fe2+ in the trivalent state V3+. This substitution is accompanied with the formation of Fe vacancies while Mn remains in the Mn2+ valence state, leading to a composition LiMn0.8Fe0.2-0.045V0.03â¡0.015PO4 where â¡ is a Fe vacancy. The comparison between electrochemical properties of a pristine sample and a sample with 3â¯mol.% vanadium made of particles with the same morphology (spherical particles with the same dispersion 100-150â¯nm in size) and same carbon coating (same conductivity of the carbon layer) is reported. Although the vanadium is in the V3+ state at open circuit voltage (2.6â¯V) before cycling, a reversible V3+/V2+ is observed when the potential of the half-cell is lowered below the redox potential of 1.8â¯V vs Li+/Li, due to Li-vacancies. The V-insertion improves the electrochemical properties, due to a synergetic effect of an increase of the lithium diffusion coefficient by a factor two and an increase of the electric conductivity at any Li-concentration during the cycling process, in contradiction with prior claims that attributed the increase of conductivity to V-based impurities.
Related Topics
Physical Sciences and Engineering
Chemistry
Electrochemistry
Authors
T. Wu, J. Liu, L. Sun, L. Cong, H. Xie, A. Abdel-Ghany, A. Mauger, C.M. Julien,