Oxidation under air of tavorite LiVPO4F : influence of vanadyl-type defects on its electrochemical properties
Résumé
Tavorite-type compositions offer a very rich crystal chemistry, among which LiVIIIPO4F has the highest theoretical energy density (i.e., 655 Wh/kg). In this article, an in-depth study of vanadyl-type defects generated by temperature-controlled oxidation of LiVIIIPO4F under air is proposed, and the influence of the defects on the electrochemical properties is demonstrated. A combination of high resolution synchrotron diffraction, infrared spectroscopy, and magic angle spinning nuclear magnetic resonance was used to fully characterize the materials thus generated, from their average long-range structure to their local structure with the presence of defects. The increase of the annealing temperature tends to substitute oxygen for fluorine with the formation of a series of LiVPO4F1–xOx compositions. The miscibility domains appear to be narrow at the two ends of the solid solution (i.e., in the composition ranges LiVPO4F[1-0.9]O[0-0.1] and LiVPO4F[0-0.1]O[1-0.9]). The presence of vanadyl-type defects obtained as localized or more extended ones, depending on the annealing conditions, affects drastically the electrochemical properties of these Tavorite LiVPO4F-type materials.
Domaines
Matériaux
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2016-179.pdf (1.82 Mo)
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2016-179-SI.pdf (944.37 Ko)
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