Lithium-Ion Batteries Working at 85°C: Aging Phenomena and Electrode/Electrolyte Interfaces Studied by XPS

Li(Ni,Mn,Co)O2/graphite lithium-ion batteries designed to work at high temperature were tested upon cycling at 85°C in various voltage ranges. Aging processes in relation with changes in the electrode/electrolyte interfaces at both electrodes were investigated by X-ray Photoelectron Spectroscopy (XPS). Changes were observed in the composition of the solid electrolyte interphase (SEI) at the surface of graphite electrode due to the high cycling temperature: disappearance of carbonates and increase of inorganic compounds coming from degradation of the salt. A slight dissolution process of the PVdF positive electrode binder was evidenced. It was also observed that the formation and thickness of the passivation layer at the positive electrode surface at 85°C depends on the cycling voltage range.