Eutectic Electrolytes Convoying Low-Temperature Metal-Ion Batteries

Eutectic electrolytes have been widely used in low-temperature metal-ion batteries (MIBs) due to their good performance regardless of seasonal and regional changes. Durable low-temperature MIBs rely on the constitution, proportion, and solvation-structure construction of eutectic electrolytes to maintain high ionic conductivity and electrochemical stability. Despite the rapid advances in eutectic electrolytes, some key issues, including fundamental mechanisms, theoretical models, aqueous/non-aqueous controversies, and challenges at sub-zero temperatures, need to be addressed. This Review first gives an overview of eutectic chemistry by presenting fundamental analysis and proposing new models to demonstrate the variety of interactions and anti-freezing mechanisms. Then, the thermodynamics and mass transfer, Helmholtz electric double-layer configuration, and electrode–electrolyte interphase are discussed to uncover the influence of the eutectic structure on the electrochemistry of low-temperature MIBs. Finally, a summary and perspectives are provided to guide the design principles and requirements of eutectic systems for applications of MIBs in low-temperature scenarios.