Deep eutectic electrolytes enable sustainable and high-performance metal-Ion batteries

Deep eutectic electrolytes (DEEs), as an emerging class of electrolytes, exhibit unique advantages through the versatileintermolecular interactions (such as hydrogen bond, van der Waals forces, etc.), including high ionic conductivity, wide-temperature adaptability, non-flammability, and considerable electrochemical stability. In this review, thefundament-als and mechanisms of DEEs are initially discussed. Subsequently, we systematically summarize recent advances in theapplication of DEEs in conventional liquid, solid-state, and aqueous metal-ion batteries (MIBs). Researches havedemon-strated that DEEs significantly improve the cycling stability and operational safety of MIBs by regulating ion solvationstructures, constructing optimized electrode/electrolyte interphases, and inhibiting dendrite growth. Moreover, thesynergistic effects of multi-component DEEs (e.g., ternary or quaternary mixtures) are further discussed. Despite thesepromising features, the practical implementation of DEEs still face challenges such as high viscosity, and issues relatedto large-scale production. Future researches are suggested to prioritize the rational design of DEEs, in-depthexplora-tion of interfacial stability mechanisms, and the development of green, scalable synthesis processes to facilitate thecommercialization of DEEs for next-generation energy storage technologies. DEEs play a critical role in enablingsustain-able and high-performance MIBs. We hope this review provides guidance to the development of DEEs in energy storagesystems.