Lithium ion electrolytes have become ubiquitous to society due to their extensive use in energy storage. However, the molecular understanding of the mechanisms giving rise to the macroscopic properties, such as conductivity, is still limited. Few studies have been able to unravel the molecular motions and mechanisms behind the dynamics of the lithium ion (Li+) solvation shell because of the complexity of these molecular systems and its ultrafast dynamics. In this work, solutions of lithium salts in acetonitrile at low and high concentrations were investigated by linear and non-linear spectroscopies in combination with ab initio molecular dynamics simulations (AIMDS). At low concentration, it is observed that the lithium ions are fully solvated by the solvent. In contrast, at high concentration Li+ is observed to be as a contact ion pair. Interestingly, the solvation shell dynamics shows a significant slowdown with concentration even though the motions of the solvation shell are similar for a free ion and a contact ion pair. AIMDS and DFT calculations revealed that the molecular mechanisms behind the dynamics at low and high concentrations have completely different origins. In the low concentration case, the motions arise from thermal fluctuations of the structure within the first solvation shell, while at high concentration the dynamics is defined by motions involving molecules and ions far beyond the first solvation shell of Li+.

Study of the structure and dynamics of the lithium salts solutions in acetonitrile at low and high concentrations

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.