An overview of deep eutectic solvents: Alternative for organic electrolytes, aqueous systems & ionic liquids for electrochemical energy storage

As the demand for sustainable energy sources continues to rise, the need for efficient and reliable energy storage systems becomes crucial. In order to effectively store and distribute renewable energy, new and innovative solutions must be explored. This review examines the deep eutectic solvents (DESs) as a green, safe, and affordable solution for the electrochemical energy storage and conversion field, offering tremendous opportunities and a promising future. DESs are a class of environment-friendly solvents known for their low toxicity and unique properties, such as their good conductivity, high thermal stability, and non-flammability. This review explores the fundamentals, preparations, and various interactions that often predominate in the formation of DESs, the properties of DESs, and how DESs are better than traditional solvents involving cost-ineffective and unsafe organic electrolytes and ionic liquids as well as inefficient aqueous systems due to low energy density for electrochemical energy storage applications. Then, a particular focus is placed on the various electrochemical applications of DESs, including their role in the electrolytes in batteries/supercapacitors, electropolishing and electrodeposition of metals, synthesis of electrode materials, recycling of electrodes, and their potential for use in CO2 capture. The review concludes by exploring the challenges, research gaps, and future potential of DESs in electrochemical applications, providing a comprehensive overview, and highlighting key considerations for their design and use.