Deep Eutectic Electrolytes for Lithium Metal Batteries: A Review

Deep eutectic electrolytes (DEEs) have emerged as highly promising materials for next-generation lithium (Li) metal batteries (LMBs), owing to the high ionic conductivity, excellent thermal stability, intrinsic flame retardance, and wide electrochemical stability window. Although the research of DEEs in LMBs is expanding rapidly, in-depth understanding of DEEs is still in their infancy. This review systematically examines the formation mechanism, classification, fundamental properties, and applications of DEEs across both liquid and solid-state LMBs. It highlights the technical advantages of DEEs in addressing critical issues such as ionic conduction, interfacial stabilization, flame retardance, and battery safety. Furthermore, future research directions are proposed, aiming at overcoming current limitations of conventional electrolytes in energy storage technology and promoting the development and practical applications of DEEs in advanced LMBs with high safe and energy density.