Molecular dynamics simulation of lithium-air battery electrolyte in high electric field

Abstract

The aqueous lithium-air battery has been receiving considerable research attention owing to its high theoretical energy density. This property is important from the perspective of enabling electric vehicles to rival the performance of gasoline-powered vehicles. However, high-power discharge has not yet been achieved. Because ion transport phenomena in the battery determine its current density, molecular interpretation of the electrolyte is required to improve battery performance. In this study, molecular dynamics simulation of LiCl electrolyte in a high-electric field was performed to elucidate the behavior of ions and molecules in the electrical double layer near the electrode. The results showed that the H₂O molecules were clearly oriented by the electric field, and Cl^- and Li⁺ formed ion-pairs or ion-clusters in the electrolyte. Those structures more easily formed under higher electric field conditions. It is considered that hydrated ion structures were difficult to form with the oriented H₂O molecules. In contrast, the highly mobile ions produced by the electric field were more likely to bond with each other. The effect of the electric field on diffusion phenomena was also investigated. Fast migration of independent ions (Cl^- and Li⁺) was caused by electrophoresis. Ion-pairs and ion-clusters were not forced to migrate because the net electric charge of the structures was zero. Our results show that a small number of independent ions play a key role in the passage of electric current through the electrolyte.