Here we are able to track the structural dynamics of how the SEI forms. The first 200 reactive cycles are dominated by the initial reduction reaction (path I), which occurs mostly as instantaneous changes in bonding topology owing to the barrierless nature of the path. Except for a few cEC •-(yellow) that sparsely populate the anode surface, the production of a high density of negative charge leads to minor exfoliation of the bulk electrolyte from the surface.