NMR evidence of LiF coating rather than fluorine substitution in Li(Ni0.425Mn0.425Co0.15)O2

Michel Ménétrier (1) , Jessica Bains (1) , Laurence Croguennec (1) , A. Flambard (1) , Emilie Bekaert (1) , C. Jordy (2) , Claude Delmas (1) , Ph. Biensan (2)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 SAFT [Bordeaux]

A series of “Li1+z/2(Ni0.425Mn0.425Co0.15)1−z/2O2−zFz” materials was prepared by a coprecipitation route and their structure was characterized using X-ray diffraction (XRD), as well as 7Li and 19F 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. 7Li and 19F 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.

Mots clés: Lithium-ion battery; Positive electrode material; Layered oxide; Li(Ni; Mn; Co)O2; Fluorine substitution; Coating; X-ray diffraction; NMR spectroscopy

Domaines: Matériaux

Michel Ménétrier, Jessica Bains, Laurence Croguennec, A. Flambard, Emilie Bekaert, et al.. NMR evidence of LiF coating rather than fluorine substitution in Li(Ni0.425Mn0.425Co0.15)O2. Journal of Solid State Chemistry, 2008, 181 (12), pp.3303-3307. ⟨10.1016/j.jssc.2008.09.002⟩. ⟨hal-00343506⟩