(30a) Electrochemical Windows of Sulfone-Based Electrolytes for Lithium Metal Batteries: A Density Functional Theory and Cluster-Continuum Model Investigation

Lithium metal batteries using lithium metal as an anode are attracting considerable interest as potential energy storage devices due to their high theoretical energy density. However, it still remains a technical bottleneck to find stable electrolyte materials that minimize the limit of selecting cathode or anode materials for high-voltage applications. Researchers report that sulfone-based electrolytes exhibit excellent oxidation stability, operating at electrochemical potentials 〉 5.0 V Li⁺/Li. Sulfone-based electrolytes still suffer from distinct problems that must be addressed before commercial applications. One primary drawback is the occurrence of excessive side reactions between sulfones and Li metal, which limit the battery life cycle. Therefore, understanding the relationship between interactions in sulfone-based electrolytes and their redox properties is of critical significance in the battery industry.

Herein, the electrochemical stability windows of sulfone-based electrolyte systems were computed using both Molecular Dynamics (MD) simulation and Density Functional Theory (DFT) calculation. MD simulation was first conducted to identify the composition of solvation structures in the electrolyte system. Then, the full-scale electrochemical windows were generated by DFT calculations. According to the cluster-continuum approach, the first solvation shell coordinated with Li cation was explicitly defined while other solvent molecules were considered using an implicit solvation model. We compared the results of two electrolyte systems with different solvents, but identical salt anion of lithium-bis(fluoromethanesulfonyl)imide (LiFSI): ethyl methyl sulfone (EMS) and dimethyl sulfone (DMS) solvent based. The electrochemical stability windows were calculated for six main coordination structures to investigate the change in values depending on the structure, levels of theory, coordination number, solvation model, and solvent type. It was confirmed that the window width widened as the empirical terms were included in the exchange-correlation functional increased. By evaluating the redox reaction through Mulliken charge analysis, it was found that fluorine dissociation generated from salt anions increases the reduction potential by stabilizing the reduction state. Defining the solvent environment in an explicit manner, a key perspective is outlined for the electrolyte design of high-performance lithium metal batteries.