XAFS and TOF–SIMS analysis of SEI layers on electrodes

Abstract We have used X-ray absorption fine structure (XAFS) in order to analyze the solid electrolyte interface (SEI) layer on the graphite anode and the LiCoO 2 cathode in a lithium-ion battery. The SEI layers on the electrodes in the propylene carbonate (PC)-based electrolyte containing an ethylene sulfite (ES) additive were analyzed based on the different sulfur oxidation states with sulfur K-edge X-ray absorption near-edge structure spectroscopy (S K-edge XANES), X-ray photoelectron spectroscopy (XPS) and time-of-flight–secondary ion mass spectrometry (TOF–SIMS). The SEI layer on the graphite anode was mainly consisted of a sulfite-type compound with an inorganic film like Li 2 SO 3 and an organic films like ROSO 2 Li. Furthermore, it was proven that the SEI layer on the graphite anode contained alkyl sulfide species. We also found that the SEI layer on the LiCoO 2 cathode also contained alkyl sulfide species.