Ionic Liquid Electrolytes for Next-generation Electrochemical Energy Devices

The development of future energy devices that exhibit high safety, sustainability, and high energy densities to replace the currently dominant lithium-ion batteries has gained significant attention in recent years. Although the various energy devices available have different technological requirements, electrolyte formulation still remains a fundamental element of these state-of-the-art systems. Among the trending electrolyte contenders, ionic liquids, which are entirely comprised of cations and anions, provide a combination of several unique physicochemical and electrochemical properties, and exceptional safety. In this review, the fundamental properties of IL, their progress and milestones, and the directions for their future development and applications in next-generation energy devices are summarized. Each section will comprehensively review the latest progress and technology trends utilizing IL electrolytes focusing on Li-, Na-, K-ion batteries, metal anode batteries, sulfur and oxygen batteries, multivalent metal-ion batteries, and supercapacitors, with early studies mentioned where relevant. The benefits of using ionic liquid electrolytes on each system and pertinent improvements in performance are delineated in comparison to systems utilizing conventional electrolytes. Finally, prospects and challenges associated with the applications of ionic liquid electrolytes to future energy devices are also discussed.