Prospects of applying ionic liquids and deep eutectic solvents for renewable energy storage by means of redox flow batteries

Ionic liquids (ILs) and deep eutectic solvents (DESs) have been applied in various fields such as electrolytes for lithium ion batteries, electrodeposition, electropolishing and even in fuel cells. ILs and molten salts have found some applications in redox flow batteries (RFBs) in the past and recently some metal ion based ILs have been proposed and used by Sandia National Laboratories. In addition, only two papers have very recently reported on the application of DESs for the same. This review gives an overview on DESs and discusses the possibility of employing them in RFBs for renewable energy storage and utility-scale load leveling applications. Commencing with a discussion on energy storage technologies and the RFB, this paper goes on to provide an account on ILs and DESs as well as their applications in electrochemistry and energy conversion. A succinct discussion on the results of Sandia National Laboratories on using ILs as electrolytes for RFBs is provided building onto the feasibility of replacing ILs with DESs in the near future (based upon recent publications on the topic).