Insights into a surface-modified Li(Ni 0.80 Co 0.15 Al 0.05 )O 2 cathode by atomic layer fluorination for improved cycling behaviour.

Li(Ni 0.80 Co 0.15 Al 0.05 )O 2 is a lithium-ion battery cathode, commercially available for more than twenty years, which is associated with high energy capacity and high energy density, with moderate power. Atomic layer fluorination (ALF) of Li(Ni 0.80 Co 0.15 Al 0.05 )O 2 with XeF 2 is performed to improve its cyclability. The ALF method aims at forming an efficient protecting fluorinated layer at the surface of the material, with a low fluorine content. Surface fluorinated Li(Ni 0.80 Co 0.15 Al 0.05 )O 2 is characterized by X-ray diffraction, electron microscopy, 19 F nuclear magnetic resonance, X-ray photoelectron spectroscopy, and galvanostatic measurements, and a fluorine content as low as 1.4 wt% is found. The presence of fluorine atoms improves the electrochemical performances of Li(Ni 0.80 Co 0.15 Al 0.05 )O 2 : cyclability, polarization and rate capability are improved. Operando infrared spectroscopy and post-mortem gas chromatography provide some insights into the origins of these improvements.