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

Water-in-salt electrolytes has received significant interest for the development of high-performance electrochemical energy storage due to their wide electrochemical stability window and high safety. However, the ion transport and charging dynamics mechanisms of water-in-salt under nanoconfinement remain poorly understood, which is crucial for the rate/power performance. 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 has been observed for highly concentrated electrolytes in subnanopore. Further analysis reveals that, contrary to bulk behavior, ion transport with enhanced solvation is strongly suppressed owing to a transition in the transport mechanism from free diffusion to oscillatory interlayer migration. Additionally, the distinctive stratification in highly concentrated electrolyte within subnanopore restricts ion adsorption and desorption to the pore entrance, yielding pronounced ion blockage. Thereby, 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 high-performance electrochemical energy storage.