Physicochemical and Electrochemical Properties of Water-in-Salt Electrolytes.

Aqueous electrolytes are attractive for applications in electrochemical technologies due to features like being eco-friendly, cost effective, and non-flammable. Very recently, superconcentrated aqueous electrolytes, such as so-called water-in-salt, water-in-bisalt, and hydrate melt, have received a significant attention for electrochemical energy storage due to enhanced stability and much wider electrochemical stability window. This Review focuses on the physicochemical properties of the highly concentrated electrolytes that are derived from several analysis techniques and simulation. A summary of most common features such as ions-water interactions, structure of species present in the electrolyte, conductivity, and viscosity of the electrolytes found in the literature are presented as well. In addition, this Review explains how these characteristics affect the electrochemical behavior of the electrolyte such as double layer structure and electrode/electrolyte interface leading to enhanced electrochemical stability of aqueous electrolytes.