An ab initio molecular dynamics study of the solvation structure and ultrafast dynamics of lithium salts in organic carbonates: A comparison between linear and cyclic carbonates

XL Zhang and DG Kuroda, JOURNAL OF CHEMICAL PHYSICS, 150, 184501 (2019).

DOI: 10.1063/1.5088820

Carbonate-based lithium-ion electrolytes are of great importance due to their close relationship with the resulting battery efficiency and safety. Modifying the organic electrolyte has been paramount for achieving more efficient and safer lithium-ion batteries. However, the molecular picture of the electrolyte is still under scrutiny. Lately, ultrafast infrared spectroscopic studies have investigated the solvation structure and dynamics of the lithium ion (Li+) in both linear and cyclic carbonates. However, theoretical studies describing the molecular arrangements and transformation occurring in such time scales are scarce. In this study, ab initio molecular dynamics simulations were used to obtain the molecular structure and dynamics of the Li+ solvation shell in cyclic and linear carbonates. The theoretical results showed that molecular arrangement of the carbonates directly coordinating Li+ is not significantly altered by the carbonate chemical nature. However, the cyclic and linear carbonates showed significant different pictures of the overall solvation shell due to the intercalation phenomenon observed for cyclic carbonates, which significantly alters the motions of coordinated solvent. In addition, the intercalation appears to affect the propensity of ion pair formation and/or solvent exchange. Finally, the dynamics of the geometrical changes of the carbonates solvating Li+ is found to occur with characteristic times of tenths of picoseconds, while ion pair and solvent chemical exchange appear to happen in time scales which are at least an order of magnitude larger. Our study provides a comprehensive picture of the structure and dynamics of the molecular components in different carbonate-based lithium-ion electrolytes occurring in picosecond time scales.

Return to Publications page