Impact of Polymer End Groups on the Formation of Solid Electrolyte Interphase at the Lithium Metal Interface: A First-Principles Calculations Study

The formation and stability of the solid-electrolyte interphase (SEI) are critical factors influencing the performance and lifespan of lithium-ion and lithium metal batteries. In this study, we employ a combination of density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations to investigate the SEI formation on Li anodes and assess the protective properties of different passivation layers. Our theoretical results confirm the experimental observations of SEI formation prior to the application of a potential difference. We examine the reactivity of four monomers representing the backbone structure of polymer electrolytes commonly used in solid-state batteries, and observe rapid decomposition triggered by charge transfer from the anode to the electrolyte. Additionally, we investigated the impact of various well-known inorganic components of the passivation layer. Among these, LiF emerges as the most effective passivation layer, potentially providing superior protection for the electrolyte and exhibiting the highest energy barrier for the detachment of reactive oxygen species. Conversely, Li2CO3 demonstrates good electrolyte protection but may exhibit limited Li ion mobility, while Li2O shows a tendency for low protection of the electrolyte. The calculated charge transfer and energy barrier data offer insights into the stability and reactivity of the SEI constituents, suggesting the potential importance of LiF in impeding electron transfer and potentially preventing further electrolyte decomposition. Our findings provide additional evidence supporting the significance of increasing the LiF content in the SEI to potentially enhance its performance.