Synthesis of “Li_1.1(Ni_0.425Mn_0.425Co_0.15)_0.9O_1.8F_0.2” materials by different routes: Is there fluorine substitution for oxygen?

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

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

A one-step synthesis method was used, with LiF or NiF₂ as fluorine precursor, to prepare Li_1.1(Ni_0.425Mn_0.425Co_0.15)_0.9O_1.8F_0.2 materials. ⁷Li and ¹⁹F magic angle spinning NMR analyses revealed the presence of fluorine as LiF at the surface of the Li(Ni_0.425Mn_0.425Co_0.15)O₂ particles, rejecting the formation of fluorine-substituted Li_1.1(Ni_0.425Mn_0.425Co_0.15)_0.9O_1.8F_0.2 materials. These results highlighted that change in cell parameters with increasing fluorine content is not by itself proof for effective fluorine substitution for oxygen in layered oxides and that heterogeneity in the transition metal and fluoride-ion distribution at the crystallite scale can be at the origin of these modifications. LiF was shown to be present as small particles in some grain boundaries but not as a continuous layer covering the particles surface. Improved cycling stability was observed for these LiF-coated materials, showing that effective fluorine substitution for oxygen is not required for improvement of the cyclability of these layered oxides; a surface modification can be sufficient and can also have a huge impact.

Mots clés: Electrochemical electrodes; Grain boundaries; Lattice constants; Lithium compound; Mmagic angle spinning; Materials preparation; Secondary cells

Domaines: Matériaux

Laurence Croguennec, Jessica Bains, Michel Ménétrier, A. Flambard, Emilie Bekaert, et al.. Synthesis of “Li_1.1(Ni_0.425Mn_0.425Co_0.15)_0.9O_1.8F_0.2” materials by different routes: Is there fluorine substitution for oxygen?. Journal of the Electrochemistry, 2009, 156 (5), pp.A349-A355. ⟨10.1149/1.3080659⟩. ⟨hal-00364482⟩