Insights into a surface-modified Li(Ni0.80Co0.15Al0.05)O2 cathode by atomic layer fluorination for improved cycling behaviour

Abstract

Li(Ni_0.80Co_0.15Al_0.05)O₂ 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_0.80Co_0.15Al_0.05)O₂ with XeF₂ 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_0.80Co_0.15Al_0.05)O₂ is characterized by X-ray diffraction, electron microscopy, ¹⁹F 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_0.80Co_0.15Al_0.05)O₂: cyclability, polarization and rate capability are improved. Operando infrared spectroscopy and post-mortem gas chromatography provide some insights into the origins of these improvements.