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 versatile intermolecular 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, the fundamentals and mechanisms of DEEs are initially discussed. Subsequently, we systematically summarize recent advances in the application of DEEs in conventional liquid, solid-state, and aqueous metal-ion batteries (MIBs). Researches have demonstrated that DEEs significantly improve the cycling stability and operational safety of MIBs by regulating ion solvation structures, constructing optimized electrode/electrolyte interphases, and inhibiting dendrite growth. Moreover, the synergistic effects of multi-component DEEs (e.g., ternary or quaternary mixtures) are further discussed. Despite these promising features, the practical implementation of DEEs still face challenges such as high viscosity, and issues related to large-scale production. Future researches are suggested to prioritize the rational design of DEEs, in-depth exploration of interfacial stability mechanisms, and the development of green, scalable synthesis processes to facilitate the commercialization of DEEs for next-generation energy storage technologies. DEEs play a critical role in enabling sustainable and high-performance MIBs. We hope this review provides guidance to the development of DEEs in energy storage systems.