High Performances of Oxyfluoride Electrode Used in Lithium Ion Battery

Abstract

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 in humid conditions. Such stability makes it possible for TiOF2 to be studied as an electrode material in Li-ion secondary batteries systems. It shows capacities as high as 220 mAh 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.