Reaction Exploration Reveals Strong Kinetic Filtering in Li-Ion Battery Electrolyte Degradation

A solid electrolyte interphase (SEI) forms spontaneously during the first few recharging cycles of a lithium-ion battery (LIB) due to electrolyte degradation at the electrodes. The properties of the SEI critically affect the lifespan and stability of LIBs, but the degradation reactions governing SEI formation are challenging to resolve and broadly applicable computational methods for prediction remain limited. In this study, we demonstrate that automated reaction exploration methods can predict major degradation products of common electrolytes without relying on experimental data, revealing unexpected kinetic filtering effects that strongly constrain the observable degradation chemistry of SEI formation. The degradation chemistry of a traditional LIB electrolyte, consisting of ethylene carbonate (EC) and lithium hexafluorophosphate (LiPF6), is analyzed out to a depth of five reactions as a benchmark. Despite the multitude of theoretically possible reaction pathways, our computational chemical reaction network (CRN) reveals strong kinetic selectivity toward lithium ethylene monocarbonate (LEMC) and lithium ethylene dicarbonate (LEDC), including several previously unreported routes to these key SEI organic species. The resulting network provides a unified explanation for how reaction barriers and kinetics drive the competing formation of LEMC and LEDC, and clarifies the influence of moisture on SEI aging. Generated entirely on the basis of computational transition state searches, this comprehensive CRN demonstrates the potential of reaction exploration methods to uncover mechanistic insights governed by kinetic filtering and enable rational electrolyte design.