Electrolyte Additives as Pathway Selectors in Early SEI Formation.

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Lithium-ion battery performance is enhanced by electrolyte additives such as fluoroethylene carbonate (FEC) and vinylene carbonate (VC).
• The precise mechanism by which these additives alter reaction pathways during solid-electrolyte interphase (SEI) formation remains under investigation.
• Understanding additive influence is crucial for designing next-generation high-performance batteries.

Purpose of the Study:

• To quantify how electrolyte composition influences structural evolution during early SEI formation.
• To determine if additives select common reaction pathways or fundamentally different decomposition channels.
• To provide a framework for rational electrolyte design in lithium-ion batteries.

Main Methods:

• Ensemble ab initio molecular dynamics simulations were employed to model SEI formation.
• Machine learning techniques, including SOAP descriptors, UMAP, and HDBSCAN, were used for structural analysis.
• 15 independent simulation trajectories across baseline, FEC-rich, and VC-rich electrolyte formulations were analyzed.

Main Results:

• Distinct, non-overlapping structural regions were identified for different electrolyte compositions.
• These regions are characterized by unique Li-O coordination environments and Li-F signatures.
• Analysis revealed emergent structural divergence during decomposition, indicating pathway selection by additives.

Conclusions:

• Electrolyte additives act as pathway selectors during the initial stages of interfacial reactions in lithium-ion batteries.
• The findings offer a quantitative framework for the rational design of advanced electrolyte formulations.
• This work elucidates the fundamental role of electrolyte composition in controlling SEI formation and battery performance.