Diverse Microstructures and Quasi-Ionic Liquid-like Transport Mechanisms in Concentrated “Water-in-Salt” Lithium Salt Electrolytes: A Molecular Dynamics Study

"Water-in-salt"(WIS) electrolytes as potential green and nonflammable electrolytes are currently applied in various energy storage devices, such as lithium-ion batteries and supercapacitors. However, the microstructure at molecular scale and fast ion transport mechanism in such aqueous electrolytes are still under heavy debate due to the complex interactions among ions and water. Here, molecular dynamics simulations are used to study the microstructure and ion transport behaviors from the very dilute LiTFSI/water solution to the highly concentrated WIS electrolytes. It revealed that the diverse microstructures such as completely hydrated ions, ion complexes, and bridge-water molecules are jointly responsible for the electrochemical stability of WIS electrolytes. Diffusion model analysis showed that the Li