Intercalation Behavior of Water-in-Salt Electrolytes in Nanoscale Hydrophobic Carbon Confinement

Abstract

Intercalation of water-in-salt (WIS) electrolytes in nanoscale confinement is an important phenomenon relevant to the energy storage applications. Here, we use enhanced sampling molecular dynamics simulations to investigate the effects of intersurface separation on the structure and free energy underlying the intercalation of the Li bis(trifluoromethane)sulfonimide ([Li][TFSI]) water-in-salt (WIS) electrolyte confined between nanoscale hydrophobic carbon surfaces. We observe that the confinement separation and the WIS concentration governs the relative stability of the condensed and vapor phases of WIS inside the confinement. The relative height of the free energy barrier separating the condensed and vapor phases of WIS also strongly depends on the concentration of [Li][TFSI] inside the confined space. We find that this concentration dependence is majorly due to changes in line tension. The process of deintercalation of electrolyte passes through a vapor tube formation inside the confined space. The size of the critical vapor tube required for spontaneous evaporation of WIS from the confinement is found to be dependent on the intersurface separation and WIS concentration.