Structural and Energetic Insights into SEI Precursors and Their Interactions in Lithium-Ion Batteries

This study employed DFT to probe the structural and energetic attributes of Solid Electrolyte Interface (SEI) precursors, notably ethylene carbonate (EC) and diethyl carbonate (DEC), both individually and in conjunction with ions such as Li⁺ and PF6⁻. Distinct changes in molecular properties such as bond lengths, angles, and dipole moments were observed upon interaction with these ions. Notably, the PF6⁻ anion profoundly influenced the solvation structures and molecular geometry of Li⁺(EC) and Li⁺(DEC). Electron behavior in these solvents was explored with an emphasis on the LUMO energy level, revealing that both Li⁺(EC) and Li⁺(DEC) possess robust electron affinities conducive to SEI formation. Comprehensive solvation energy evaluations indicated a synergistic energy enhancement when using EC and DEC together, although this was significantly attenuated in the presence of the PF6⁻ anion. Further insights from Gibbs free energy assessments underscored the structural stability of the Li⁺(EC) complex, particularly without PF6⁻. Complementing these findings, adsorption studies on bilayer graphene illustrated that the introduction of lithium amplifies adsorption energy, highlighting its pivotal role in the SEI formation in lithium-ion batteries. Nevertheless, the incorporation of PF6⁻ decreased this adsorption energy, suggesting a mediating effect between Li⁺ and PF6⁻in their interaction with graphene. Collectively, this work elucidates the multifaceted interactions and potential implications of these solvents and ions in SEI layer development.