Dynamic Water Promotes Lithium-Ion Transport in Superconcentrated and Eutectic Aqueous Electrolytes

Superconcentrated aqueous electrolytes have shown promise as safe and high-voltage lithium-ion battery (LIB) electrolytes. However, the interplay of lithium-ion solvation structure and dynamics with fast Li-ion transport has not been elucidated yet. Here, we combine the ultrafast femtosecond mid-IR spectroscopy, dielectric relaxation spectroscopy, pulsed-field gradient NMR, and molecular dynamics simulation for investigating the solvation structure and Li-ion transport mechanism in superconcentrated aqueous electrolytes. We found the existence of water molecules with vibrational and rotational properties very similar to those of bulk water, even at extremely high salt concentrations (28 m). Our experimental results show that the electrolytes have a heterogeneous solvation environment, and bulk-like water molecules promote fast Li-ion transport. We anticipate that the molecular understanding of the superconcentrated aqueous electrolytes obtained here would facilitate the design of solvation structures to overcome the limit of dilute LIB electrolytes.

Automated summary

This study investigated the solvation structure and Li-ion transport mechanism in superconcentrated aqueous electrolytes using various techniques. The results showed that even at extremely high salt concentrations, water molecules exhibit properties similar to bulk water, and the electrolytes have a heterogeneous solvation environment that facilitates fast Li-ion transport. The findings suggest potential for designing solvation structures to improve the performance of dilute LIB electrolytes.