Super-slow charging dynamics of water-in-salt electrolytes in subnanopore

Water-in-salt electrolytes have attracted significant interest as high-performance electrolytes for electrochemical energy storage owing to their expanded electrochemical stability windows and enhanced safety. However, the mechanisms of ion transport and charging dynamics of water-in-salt electrolytes under nanoconfinement remain poorly understood. Here, we employed constant-potential-based molecular dynamics simulations to investigate ion transport and charging dynamics of water-in-salt electrolytes within subnanopore. In contrast to dilute solutions, an anomalous solvation-enhancement phenomenon was observed for highly concentrated electrolytes in subnanopore. Further analysis reveals that, contrary to bulk behavior, ion transport with enhanced solvation is strongly suppressed, ascribable to a transition in the transport mechanism from free diffusion to oscillatory interlayer migration. Additionally, in highly concentrated electrolytes within subnanopore, the distinctive layered structure restricts ion adsorption and desorption to the pore entrance during charging, ultimately yielding pronounced ion blockage. As a result, the charging rate of high-concentration electrolytes is reduced by nearly an order of magnitude relative to dilute solutions. These findings provide valuable insight into ion transport in water-in-salt electrolytes under nanoconfinement and offer theoretical guidance for the design of next-generation electrochemical energy storage systems.