Physicochemical and Electrochemical Properties of Water‐in‐Salt Electrolytes

• Published in: ChemSusChem Vol. 14; no. 12; pp. 2487 - 2500
• Main Authors: Amiri, Mona, Bélanger, Daniel
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 21.06.2021
• Subjects: Aqueous electrolytes; Electrochemical analysis; Electrochemistry; Electrolytes; Energy storage; Flammability; highly concentrated solution; Interface stability; physicochemical properties; water-in-salt; Electrochemistry; water-in-salt; physicochemical properties; electrolytes; highly concentrated solution
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.202100550

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. A grain of salt: Highly concentrated aqueous electrolytes with salt‐to‐water ratio well above conventional electrolytes demonstrate promising potential for use in electrochemical energy storage devices. This is mainly caused by presence of minimal free water and leads to divergence of their physicochemical and electrochemical features from dilute electrolytes. This Review covers the variation of these properties using simulation and several analysis techniques.