Fluorination of MXene by Elemental F as Electrode Material for Lithium-Ion Batteries.

The transformation of MXene sheets into TiOF 2D sheets with superior electrochemical performance was developed. MXene synthesized from Ti AlC was fluorinated for 3, 6, and 24 h, respectively, by means of a direct fluorination process. Exposure of MXene powder to elemental fluorine for 3 h induced the formation of CF groups and TiF on the surface, which have beneficial effects on the electrochemical performance. X-ray photoelectron spectroscopy suggested that after fluorinating the MXene sample for 6 h Ti and Ti were not present on the surface but only Ti , indicating the formation of TiOF . XRD indicated that TiOF was present after fluorinating for 3 h, and after 24 h the MXene had transformed to TiOF with minor impurities remaining, maintaining its 2D layer morphology. The 24 h fluorinated sample with its TiOF phase showed superior capacity that increased with cycle number. It also had a better rate capability than non-2D-layered TiOF , indicating the advantage of the 2D-layered morphology derived from the parent MXene phase.