Unravelling multi-layered structure of native SEI on lithium metal electrode and various electrolytes using reactive molecular dynamics

Lithium metal batteries, directly utilizing lithium metal as an anode, are promising as new-generation energy storage devices, and the characteristics of the solid electrolyte interphase (SEI) layer are critical to battery operation. However, the roles of electrolyte compositions on the structure and thickness of the passivating SEI film at the atomistic level have been previously overlooked, resulting in poor understanding of SEI characteristics. In this study, the formation of the native SEI layer on lithium metal electrode and various electrolyte composition is scrutinised using ReaxFF molecular dynamics (MD) simulations. The study successfully identifies different layers of the SEI film using charge distribution as a tool. The decrease in lithium density and the increase in the charge states of oxidised lithium atoms contribute to the identification of an inner layer and a transition layer within the previously known interface layer, as well as the sparse layer. Additionally, different reaction schemes are observed through the analysis of ratio between consumed lithium atoms and electrolyte molecules. Furthermore, results show the lithium salt concentration effects in suppressing the growth of the SEI between the lithium anode and the liquid electrolyte, and inhibiting the formation of key SEI components. This work provides new insights into the nature of SEI surface chemistry and potentially facilitates the design of artificial SEI layers and optimal electrolyte solutions. • Identification of the multi-layered SEI film using charge distribution as a tool. • Variations in lithium density and charge states of oxidised lithium atoms contribute to layer identification. • Different reaction schemes observed through consumed Li-Electrolyte ratio analysis. • SEI spatial distribution analysis provides insights for migration/expansion pathway. • Lithium salt concentration contributes to inhibit formation of key SEI components.