Suppression of irreversible capacity loss in Li-rich layered oxide by fluorine doping

Li[Li1/6Ni1/6Co1/6Mn1/2]O2-xFx (x = 0.00 to 0.07) materials were synthesized with low temperature heat treatment (700 °C) and their electrochemical performances were evaluated. With the addition of fluorine, the reversible capacity significantly increased as the irreversibility was suppressed during the first cycle. The reduction of irreversibility was mainly attributed to the enhanced first cycle efficiency of Li2MnO3-like component after the fluorine addition. By combining results of the X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), In-situ X-ray absorption spectroscopy (XAS) analyses, and first principle calculations, it was proposed that the presence of fluorine facilitated the reduction of cobalt and manganese ions in Li-rich layered oxide, and that the reduced transition metal (TM) ions suppressed structural changes. [Display omitted] •Fluorine doped Li-rich cathode showed greatly reduced first cycle irreversibility.•The improvement was due to the increased Li reinsertion efficiency of Li2MnO3.•In-situ XAS indicated that Mn and Co ions were reduced after the fluorination.•The structural stability of Li2MnO3 was enhanced by the reduced metal ions.