XANES study on solid electrolyte interface of Li ion battery

We have investigated solid electrolyte interfaces (SEI) of lithium ion batteries containing sulfur additive for electrolyte with S K-edge XANES spectra. Graphite anode and LiCoO2 cathode were used as electrodes and ethylene sulfite (ES) was used as an additive for propylene carbonate electrolyte. Compared with XANES spectra of standard compounds, it is elucidated that the SEI layer on the graphite anode includes Li2SO3, ROSO2Li, Li2SO4 and organic sulfur with C-S-C and/or C-S-S-C bonding. The XANES spectrum of the cathode shows that Li2SO4 and organic sulfur compounds with C-S-C and/or C-S-S-C are included in the SEI on the cathode. In the discharge state, the sulfur compounds in SEI layers on the anode dissolve into the electrolyte under high temperature around 120 degrees C although the dissolution of the sulfur species is not observed in the charge state. On the other hand, it is found that the rate of dissolution of the sulfur compounds in SEI layers on LiCoO2 cathode is lower in the discharge state than in the charge state.