Composition, depth profiles and lateral distribution of materials in the SEI built on HOPG-TOF SIMS and XPS studies

The importance to study separately the composition and properties of the solid electrolyte interphase (SEI) on basal and cross-section planes of graphite particles is demonstrated. The lateral distribution of SEI forming compounds at submicron resolution is presented for the first time. It was found that Li and F are the main constituents of the SEI cross-section. The SEI on the solution-side surface of the basal plane contains much more organic materials than that of the cross-section one. The SEI on the HOPG can be described as non-homogeneous. The SEI cross-section is dominated by Li and F, with one to several dozen micron-sized regions where Li and F are almost absent. The distribution of C2H (and other CxHy-based fragments), O, C2H3O2 (59), and C2H3O (43), shows full coverage and is fairly homogeneous. The true lateral size of the microphases is about 1 μm. TOF SIMS measurements provide direct evidence for the existence of polymers in the basal SEI.