Aone-step synthesis method was used, with LiF or NiF₂ asfluorine precursor, to prepare Li_1.1(Ni_0.425Mn_0.425Co_0.15)_0.9O_1.8F_0.2 materials. ⁷Li and ¹⁹F magicangle spinning NMR analyses revealed the presence of fluorine asLiF at the surface of the Li(Ni_0.425Mn_0.425Co_0.15)O₂ particles, rejecting theformation of fluorine-substituted Li_1.1(Ni_0.425Mn_0.425Co_0.15)_0.9O_1.8F_0.2 materials. These results highlighted that changein cell parameters with increasing fluorine content is not byitself proof for effective fluorine substitution for oxygen in layeredoxides and that heterogeneity in the transition metal and fluoride-iondistribution at the crystallite scale can be at the originof these modifications. LiF was shown to be present assmall particles in some grain boundaries but not as acontinuous layer covering the particles surface. Improved cycling stability wasobserved for these LiF-coated materials, showing that effective fluorine substitutionfor oxygen is not required for improvement of the cyclabilityof these layered oxides; a surface modification can be sufficientand can also have a huge impact.< Leer menos