In Operando XRD/Electrochemistry Investigation of Lithium Insertion into Anatase-Derived Titanium Oxyfluoride TiOF2

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 an air-stable oxyfluoride that is a potential electrode material for Li-ion secondary batteries systems. It shows capacities as high as 220 mAh g^-1 and good cyclability at  high current rates in a potential window of 4-1.2V. In such window, only Li⁺ insertion occurs, as proven by in operando XRD/electrochemistry experiments.