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

• Published in: Journal of solid state chemistry 2008-12, Vol.181 (12), p.3303-3307
• Main Authors: MENETRIER, M, BAINS, J, CROGUENNEC, L, FLAMBARD, A, BEKAERT, E, JORDY, C, BIENSAN, Ph, DELMAS, C
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical Sciences; Condensed matter: structure, mechanical and thermal properties; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; Cross-disciplinary physics: materials science; rheology; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Exact sciences and technology; Material chemistry; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Structure of solids and liquids; crystallography
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2008.09.002

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.