Investigating the pressure-induced evolution of solid electrolyte interphase on Li metal anodes: A ReaxFF molecular dynamics study

The stability and functional characteristics of the solid electrolyte interface (SEI) membrane have a decisive impact on the overall performance of battery. In this study, the simulation approach of reactive force field molecular dynamics (ReaxFF-MD) was employed to comprehensively investigate how pressure affects the dynamic growth, structural changes, and property transitions of the SEI membrane in lithium metal batteries (LMBs). The application of a coordination number-based method to identify the SEI membrane significantly improved the precision of analyzing the physical and chemical property impacts under varying pressurized conditions. This research extensively quantified key parameters of the SEI membrane under different pressures, such as thickness, volume, density, gas generation and porosity. It revealed a significant influence of pressure on the structure and performance of the SEI membrane. It was observed that increased pressure contributes to the formation of thinner and denser SEI membranes, effectively promoting the stratification and densification of the SEI membrane structure. Experimental X-ray photoelectron spectroscopy (XPS) characterization indicated that increasing pressure offers assistance in enhancing the yield of inorganic compounds like LiF, thereby favorably improving the mechanical properties of the SEI membrane. However, pressurization narrows the lithium ion transport channels within the SEI membrane, negatively impacting the rate of lithium ion transmission. The research employed a phase field model to simulate the growth process of lithium dendrites, considering the effects of external pressure and microstructure of the SEI membrane on lithium dendrite growth. The results demonstrated that the dense structure of the SEI membrane under external pressure effectively inhibits the growth of lithium dendrites. In conclusion, this paper reveals the delicate balance among pressures, lithium ion transport characteristics, mechanical properties of the SEI membrane and the growth of lithium dendrites. Despite the potential enhancement of the mechanical performance and stability of the SEI membrane and the suppression of lithium dendrite growth under pressure, excessively high pressure can impede lithium ion transport rates, adversely affecting the electrochemical performance of battery. Therefore, we emphasize the necessity of finding a precise balance among various parameters under external to ensure optimal battery performance.