Fluorination of anatase TiO2 towards titanium oxyfluoride TiOF2: a novel synthesis approach and proof of the Li-insertion mechanism

International audience; The reactivity of pure molecular fluorine F2 allows the creation of new materials with unique electrochemical properties. We demonstrate that titanium oxyfluoride TiOF2 can be obtained under molecular fluorine from anatase titanium oxide TiO2, while the fluorination of rutile TiO2 leads only to pure fluoride form TiF4. Contrary to most fluorides, TiOF2 is air-stable and hydrolyses poorly under humid conditions. Such a stability makes it possible for TiOF2 to be studied as an electrode material in Li-ion secondary battery systems. It shows the capacity as high as 220 mA h g−1 and good cyclability at high current rates at an average potential of 2.3 V vs. Li+/Li. At such a potential, only Li+ insertion occurs, as proven by in operando XRD/electrochemistry experiments.