NMR evidence of LiF coating rather than fluorine substitution in Li(Ni0.425Mn0.425Co0.15)O2
✍ Scribed by M. Ménétrier; J. Bains; L. Croguennec; A. Flambard; E. Bekaert; C. Jordy; Ph. Biensan; C. Delmas
- Publisher
- Elsevier Science
- Year
- 2008
- Tongue
- English
- Weight
- 562 KB
- Volume
- 181
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
A series of ''Li 1+z/2 (Ni 0.425 Mn 0.425 Co 0.15 ) 1Àz/2 O 2Àz F z '' materials was prepared by a coprecipitation route and their structure was characterized using X-ray diffraction (XRD), as well as 7 Li and 19 F Magic Angle Spinning (MAS) NMR spectroscopy. Two hypotheses were considered: (i) formation of layered oxyfluoride materials and (ii) formation of a mixture between the layered material and LiF. Structural parameters were refined by the Rietveld method, using XRD diffraction data. The refinement results did not allow us to choose between these two hypotheses: no significant change in crystallinity and structural parameters was observed irrespective of the fluorine ratio. 7 Li and 19 F MAS NMR analyses showed signals with isotropic positions characteristic of LiF, but envelopes characteristic of very strong dipolar interactions with the electron spins of the material, demonstrating that LiF was not incorporated into the layered oxide structure but was instead present as a coating.