Thermal stability of the solid electrolyte interface (SEI)-layers formed on graphite, mesocarbon microbeads and carbon-black anodes is shown to be dependent on the type lithium salt used in the electrolyte. Exothermic breakdown of the passivation layers formed on cycled electrodes using LiCF3SO3 or LiN(CF3SO2)2 in EC/DMC electrolyte solutions is compared on the basis of DSC, XPS and confocal Raman spectroscopy measurements. Lithium ions in intercalated carbon electrodes are shown not to be involved in the exothermic reactions below 250°C. However, changes are observed in the chemical composition of the SEI-layers using XPS on electrodes stored at 150°C.