Electrolyte Additives as Pathway Selectors in Early SEI Formation

molecular dynamics simulations coupled with machine learning structural analysis quantify how electrolyte composition controls access to configuration space during early solid-electrolyte interphase (SEI) formation. Analysis of 15 independent trajectories across baseline, FEC-rich, and VC-rich formulations using SOAP descriptors, UMAP, and HDBSCAN reveals that each composition occupies nonoverlapping structural regions characterized by distinct Li-O coordination environments and composition-dependent Li-F signatures. Diagnostic comparison of initial and evolved configurations, including Li-centered SOAP descriptors that isolate emergent structural changes from compositional encoding, and supported by time-resolved SOAP analysis, provides evidence that this separation reflects emergent structural divergence during decomposition. These results suggest that electrolyte additives function as pathway selectors during early interfacial reaction, offering a framework for rational electrolyte design.