Effect of carbon substrate on SEI composition and morphology

The composition and morphology of the solid electrolyte interphase (SEI) formation on highly ordered pyrolytic graphite (HOPG), SLX20-graphite and disordered-carbon electrodes was studied by the XPS and TOFSIMS methods. The experimental data show good evidence for compositional and morphological distinctions between the SEI formed on the basal and cross-sectional planes of graphite. The basal plane film was found to be enriched in organic compounds, but was relatively thinner than that of the cross-section, which contained predominantly salt-reduction products. The SEI formed in LiAsF₆ and LiTFSI electrolytes is thinner than that in LiPF₆ electrolyte on all the carbon substrates. The SEI on hard carbon is thicker than on soft in all the electrolytes studied. The SEI composition on the hard carbon with high content of salt-reduction products, is similar to that formed on the cross-section of HOPG. The SEI composition on soft carbon has some similarity to that formed on the basal plane of HOPG.