Electrode Potential Effect on the Structures, Properties, and Formation Process of SEI Film in Lithium-Ion Batteries: Red Moon Analysis

In this study, we conducted simulations to explore the formation of solid electrolyte interphase (SEI) films in a lithium-ion battery (LIB) system containing 1.1 M lithium hexafluorophosphate (LiPF₆) and ethylene carbonate (EC) at different electric potential (EP) differences (1.0, 2.0, 3.0, and 4.0 V). Using the Red Moon (RM) method combined with the constant-EP approach, we observed a decrease in the fractional accessible volume (FAV) of the SEI films as the EP difference increased. These findings suggest that the SEI film formed at an EP difference of 4.0 V exhibits the longest lifespan. The longevity of the battery can be attributed to the increased frequency of the dimerization reaction of the reduction product of EC with this EP difference. Our observations also show that the increased EP difference results in a greater negative charge on the anode, attracting more EC molecules from the initial stages of the formation process. As a result, this increase amplifies the total number of chemical reactions within LIBs. Our study highlights the importance of the proportion of chemical reactions during the initial stages of the SEI film formation process in determining its ultimate structure and properties. Therefore, it is crucial to regulate these reactions to control the SEI film properties. This information could have an impact on the design and optimization of LIB systems and provide ways to customize the SEI film properties, improving battery performance and lifespan.