Recent advances in deep eutectic solvents for next-generation lithium batteries: Safer and greener

Deep eutectic solvents (DESs), renowned for their cost-effectiveness and eco-friendliness, have attracted widespread attention in the field of energy storage, especially for lithium-ion batteries (LIBs). By virtue of its environmental adaptability, superior safety, and effortless production with low cost, it provides the possibility to alleviate the notorious safety issues associated with LIBs, as well as the environmental problems caused by the high toxicity of electrolytes. Given that, it is massively argued that cost-effective DESs may serve as a feasible substitute for ionic liquids in the formulation of electrolytes and electrodes for LIBs. Therefore, despite the fact that the relevant research is still in its infancy, there has been a proliferation of studies on the application of DESs to LIBs in recent years. However, the drawbacks of DESs, such as the high viscosity, pull down the upper limit of their electrochemical performance, limiting the potential for large-scale application as well as troubling the research of relevant scholars. Thereupon, a thorough and critical review of the recent progress in applying DESs for LIBs is essential for advancing this emerging research field. This paper, therefore, investigates the transport mechanism of Li⁺ in liquid electrolytes of DESs, provides insights into the interfacial challenges in solid electrolytes of DESs, focuses on the role of DESs in electrode synthesis, and compares the electrochemical performance of DESs with that of ionic liquids (ILs). Finally, this paper discusses the challenges faced by the application of DESs in LIBs, and proposes possible future directions, such as the development of novel DESs systems and the modulation of the interrelationships between the components and electrochemical properties of existing DESs systems, hoping to provide guidance for the relevant studies in the promotion and development of DESs in LIBs.