Formation of SEI on cycled lithium-ion battery cathodes - Soft X-ray absorption study

The formation of a solid electrolyte interface (SEI) on LiNi0.85Co0.15O2 cathodes front lithium-ion cells cycled at 40 and 70 degreesC was observed and characterized using soft X-ray absorption spectroscopy (XAS). XAS Measurements were made in the energy region between 500 and 950 eV. encompassing the Ni and Co L3- and L-2-edges and at the K-edges of O and F. Measurements, obtained in the total electron yield mode, are surface sensitive, probing to a depth of 5 rim, XAS at the F K-edge demonstrates the presence of poly(vinylidene fluoride) (PVdF) in addition to LiF oil the surface of cycled electrodes. The results indicate that the PVdF in the cycled electrodes is largely intact and that the LiF comes front decomposition of LiPF6 from the electrolyte XAS also suggests Fe contamination of cycled cathodes. (C) 2001 The Electrochemical Society.