Calendar and cycle life of lithium-ion batteries (LIBs) are predominantly dictated by the passivating nature of the solid electrolyte interphase (SEI) film growth on battery anodes. Graphitic anodes exhibit stable SEI growth which enables ubiquitous commercialization of LIBs. In contrast, silicon anodes exhibit poorly passivating SEI characteristics including rapid thickness and composition changes during cycling (“breathing”) and sensitivity to electrolyte composition and surface functionalization. In this work, we develop a chemically complex continuum-level multicomponent, multiphase coupled thermodynamics-reaction-transport SEI model to unravel the mechanisms of SEI growth in LIB anodes. Atomistic calculations in conjunction with experimental datasets are utilized to ascertain the dominant decomposition pathways towards predominant SEI components like Li₂EDC, Li₂O, Li₂CO₃, LiMC, LiF etc. and inform the continuum model predictions. Furthermore, experimental voltage-hold measurements are utilized to validate the SEI model parasitic currents/composition evolution profiles enabling prediction of voltage regimes for stable SEI growth with favorable SEI composition. The development of such chemically complex SEI models will aid predictive electrolyte screening for the growth of stable and passivating SEI layers on next generation anodes like silicon.

Figure 1(a) shows a schematic of the detailed SEI model incorporating species and charge transport through the pore and solid phases of the SEI for LEDC formation. Figure (b) showcases experimental leakage currents during V-hold at 100 mV and 250 mV for Li-Si half cells and the detailed SEI model fits. Figure (c) shows the SEI composition profiles predicted by the model and the formation of inner inorganic (Li₂CO₃, Li₂O) - outer organic (LEDC) bilayer SEI. Interestingly, inorganic LiF from FEC decomposition is predicted to form throughout the SEI.