Electrical Double Layer Structure in Ionic Liquids and Its Importance for Supercapacitor, Battery, Sensing, and Lubrication Applications

Ionic liquids (ILs) have become highly popular solvents over the last two decades in a range of fields, especially in electrochemistry. Their intrinsic properties include high chemical and thermal stability, wide electrochemical windows, good conductivity, high polarity, tunability, and good solvation properties, making them ideal as solvents for different electrochemical applications. At charged surfaces such as electrodes, an electrical double layer (EDL) forms when exposed to a fluid. IL ions form denser EDL structures compared to conventional solvent/electrolyte systems, which can cause differences in the behavior for electrochemical applications. This Perspective discusses some recent work (over the last three years) where the structure of the EDL in ILs has been examined and found to influence the behavior of supercapacitors, batteries, sensors, and lubrication systems that employ IL solvents. More fundamental work is expected to continue in this area, which will inform the design of solvents for use in these applications and beyond.