In that picture, the resulting products and thus the composition of the initial SEI depend on the extent of activation, as indicated by the different compositions of the adlayer after annealing to increasing temperatures. Previous studies of SEI formation in BMP-TFSI based electrolytes had shown that mainly inorganic binary compounds, in particular LiF, were present in the range close to the electrode -SEI interface, reflecting complete decomposition of the TFSI. In contrast, the range more away from that interface was increasingly dominated by organic species, indicating incomplete decomposition of the TFSI. This structure must be due to a change in experimental conditions with increasing SEI thickness, e.g., in the chemical activity of the surface of the growing SEI or in the local concentration of different species during the SEI formation process. Alternatively, it could be caused by a change in the local potential due to a potential drop over the SEI, leading to a change in electrochemical activation of the decomposition process, which becomes less effective with increasing thickness of the SEI and thus decreasing potential difference between SEI and electrolyte. In total, we propose a more chemical picture of the SEI formation than models based on electron transfer induced reduction of the electrolyte, as already suggested for other systems, and model studies like the present one can lead to a comprehensive understanding of the chemical reactions going on during SEI formation.