Atomistic Insights into the Decomposition of Solid Polymer Electrolyte Molecules on Lithium Metal Anode: A Combined DFT and AIMD Study

Lithium metal anodes hold great promise for high-energy batteries but are hindered by uncontrolled dendrite growth and unstable solid-electrolyte interphase (SEI) formation. This study explores the early molecular interactions at the lithium-electrolyte interface, providing theoretical insights into potential reaction pathways prior to SEI formation. In the present work, ab initio molecular dynamics and density functional theory simulations are employed to investigate the interactions and decomposition of solid polymer electrolyte molecules on lithium metal anode surfaces. The electrolyte comprises polyvinylidene fluoride, fluoroethylene carbonate, and lithium bis(fluorosulfonyl)imide. By analyzing adsorption energies, Bader charges, charge density differences, and projected density of states, we identify the most favored pathways of decomposition. A study of the decomposition of a fluorinated electrolyte at the surface of two lithium electrode planes, Li(100) and Li(110), was conducted. It was found, through differences in relative energies, that reduction pathways on the Li(110) surface are more favorable than those on the Li(100) surface. Specifically, for the system involving the solvent, the salt, and the polymer, it was found to be more favorable by 0.16, 0.23, and 0.26 eV, respectively. Moreover, the simulations unveil the formation of crucial SEI components, such as LiF, which is known to promote uniform lithium deposition and mitigate dendrite growth. The good agreement between our findings and previous experimental studies underscores the robustness of the employed theoretical approach. The insights gained from this comprehensive atomistic study provide valuable guidance for optimizing solid polymer electrolyte chemistry and structure to enable high-performance lithium metal batteries.