Abstract:

Electrolyte is an important part of electrochemical energy storage (EES) equipment that plays a decisive role in device performance. Among a wide variety of electrolytes, water-in-salt (WIS) electrolyte has expanded the electrochemical window of an aqueous solution to above 3.0 V by the virtue of its unique solvent coordination ability. WIS has the advantages of aqueous electrolytes safety, low cost, and environmental protection which is very promising in future applications. The latest research of WIS electrolytes was reviewed here and abroad, including electrolyte salts, electrolyte additives, the application of WIS electrolytes in electrochemistry, and its problems and challenges. For the electrolyte salts, several common fluorides based on sulfonimide and acetate such as potassium acetate, sodium acetate, and lithium acetate are described. The influence of WIS electrolyte prepared in the form of single or multiple salts on the electrochemical performance of capacitors and batteries has been analyzed. The electrolyte additives mainly include acetonitrile (AN), dimethyl carbonate (DMC), propylene carbonate, and other organic solvents, and introduce ionic liquids and carboxymethyl cellulose (CMC) as a cosolvent to improve the performance of electrode materials. The application of WIS electrolyte focuses on the electrode materials which cannot be used in conventional electrolytes or with poor performance, and in the derived solvent-in-salt system. Finally, the current problems and challenges faced by WIS electrolyte and the research directions of this electrolyte are proposed.

Key words: electrolyte, water-in-salt, supercapacitor, battery, electrochemical performance