Nanostructured Iron Trifluoride from the Fluorination of Iron Silicide

Metal fluorides are low cost inorganic compounds that have been studied for their industrial applications such as smelting in metallurgy, uranium enrichment processor optical material production. This applied development of the synthesis of inorganic fluorides allowed intense fundamental researches in the 70’s and 80’s as regards their electronic, and more particularly magnetic, properties. In the last decades, research subjects have been shifted toward the nanostructuration of inorganic fluorides, due to potential applications such as in secondary lithium battery. Indeed, nanostructured metal fluoride materials are potential candidate materials as cathodes for lithium-ion batteries through both insertion and conversion reactions and they could improve the theoretical specific capacity of the positive electrode.

Among the MF₃ fluorides (M = metal), iron trifluoride, FeF₃, is one of the most promising candidate. However, its application as a cathode material for lithium ion battery has been largely hindered by both its low conductivity and its high sensibility to air humidity leading to cyclability rather limited. This work will present some new strategies to develop nanostructured iron fluoride of high chemical stability. They have been prepared through the reactivity of some unusual metal precursors with molecular fluorine gas. In order to favor the nanostructuration of the metal fluoride, the kinetic of fluorination has been followed by in-situ Infra-Red measurements. All the metal fluorides obtained have been then characterized by Scanning Electronic Microscopy, XRD, IR, MOSSBAUER, and Raman spectroscopies. Finally, the electrochemical performances will be presented and correlated with both the fluorination conditions and the physicochemical characteristics of the samples prepared.