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Final Report Summary - FLUOSYNES (New nanosized metal oxy-FLUOrides: tailored SYNthesis and Energy Storage)

The scientific activities of the FLUOSYNES project were focused on the development of new chemical routes for the preparation of nano-sized particles of transition metal oxyfluoride with a particular interest on iron and titanium based compounds. The major activities can be summarized by the following tasks:
- Development of new chemical routes for the synthesis of mixed anionic oxyfluorinated compounds with a particular interest on the understanding of the crystal formation mechanism;
- key physico-chemical and structural characterization of new prepared compounds with the aim to provide new structural and spectroscopic signatures further allowing the optimization of the material’s properties;
- Assess the properties of the prepared compounds in the field of energy storage, in particular their uses as electrodes in electrochemical devices such as batteries.

Two different synthesis strategies were adopted for the synthesis of titanium and iron-based compounds which are:
i) titanium-based compounds: sol-gel chemistry performed in the presence of a fluorinating agent;
ii) iron-based compounds: controlled thermal decomposition of an iron fluoride hydrate.

i) By using sol-gel chemistry, we investigated the impact of using a fluorinating medium in the stabilization of titanium dioxide compounds. We demonstrated that the use of such a reaction system led to the stabilization of a mixed anionic compound where oxide are partially by fluoride and hydroxide anions with the concomitant formation of titanium vacancies. The formation mechanism of this compound revealed that titanium alkoxide undergoes both hydrolysis and fluorolysis yielding an anatase phase with a hydroxyfluoride composition which further evolved into an oxy-hydroxyfluoride phase by oxolations reactions. Moreover, the impact of the solvent characteristics and fluorine concentration has been investigated with respect to the structure/composition of the stabilized phases and were shown to be decisive parameters. This study further proves the complexity of such a system and provides novel tools to optimize the material’s properties by tuning the composition and morphology of Ti-based compounds.

(ii) Iron oxyfluoride featuring anionic vacancies was prepared by the thermal decomposition of an iron fluoride hydrate precursor. A comprehensive investigation of the structure and thermal behavior of the precursor was undertaken and enabled to develop a controlled decomposition process to yield In a this scope, we started from an iron fluoride hydrate and developed a decomposition process to an iron oxyfluoride featuring an hexagonal-tungsten-bronze structure containing anionic vacancies. We further highlights the fact the precursor can be produced from the pickling liquor from the steel industry.

Iron and titanium oxyfluoride compounds have been studied as electrode materials for lithium batteries. They exhibited remarkable properties which have been related to the material’s characteristics, i.e., presence of vacancies. To do so, very fine characterization of the material was performed and the lithium storage mechanism has been established.

Damien Dambournet
Sorbonne Universités, UPMC Univ Paris 06, CNRS, Laboratoire PHENIX, Case 51, 4 place Jussieu, F-75005 Paris, France.

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Anaïs DESCLOS, (European project officer)
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