Abstract: With the rapid iteration of the new energy industry, lithium-ion batteries (LIBs) have been extensively applied in fields such as electric vehicles and energy storage devices. However, constrained by the lagging recycling modes, the global annual output of spent LIBs has exceeded one million tons. Spent LIBs contain scarce metals like cobalt, nickel, and lithium, as well as toxic components including electrolytes and binders. Improper disposal of these spent batteries is prone to causing resource waste and pollution to soil and water bodies. Therefore, the efficient recycling and reuse of spent LIBs have become a strategic priority for safeguarding resource security and promoting the achievement of the "dual carbon" goals. As a new type of green solvent formed by mixing hydrogen bond donors and acceptors in a specific ratio, deep eutectic solvents (DESs) have gradually replaced traditional toxic and volatile solvents. Endowed with prominent advantages such as excellent environmental compatibility, strong recyclability, tunable physicochemical properties, and outstanding dissolution capacity for cathode metal oxides, DESs have demonstrated significant practical value and economic feasibility in the field of spent LIBs recycling. This paper systematically combs the research status of spent LIBs recycling using DESs in recent years, focusing on elaborating the extraction mechanisms and core principles of valuable metals from battery cathode materials. Meanwhile, it deeply analyzes the separation principles of different DESs systems and clarifies the differences in their core leaching mechanisms. In the process of exploring DESs-based recycling technologies, the separation efficiency and leaching mechanism of each system are closely related to its composition and structure. For example, hydrogen bond-based DESs mainly rely on hydrogen bond interaction to promote the dissolution of metal oxides, while metal-based DESs may enhance leaching efficiency through synergistic effects between metal ions and target metals. By clarifying these mechanism differences, it can provide a theoretical basis for the targeted design and optimization of DESs systems. On this basis, the paper further discusses the bottleneck problems faced by the current DESs recycling technology. At present, although DESs have shown great potential in laboratory research, there are still many challenges in practical application. For instance, the preparation cost of some high-performance DESs is relatively high, which restricts their large-scale promotion; in addition, the viscosity of partial DESs is too high at room temperature, which affects the mass transfer efficiency of the leaching process and reduces the overall recycling efficiency. Moreover, the separation and purification technology of target metals in DESs leaching solutions needs to be further improved to realize the efficient recovery of valuable metals. Finally, the paper prospects the future technical paths for efficient, green, and sustainable recycling of spent LIBs using DESs. It is proposed that future research should focus on the development of low-cost DESs systems, explore the use of cheap raw materials such as biomass derivatives to reduce preparation costs, and optimize the composition ratio of DESs to adjust their physicochemical properties and improve leaching performance. At the same time, it is necessary to strengthen the research on multi-metal synergistic separation technology to realize the selective recovery of various valuable metals in spent LIBs. In addition, constructing an integrated process of "leaching-separation-regeneration" is also an important development direction, which can realize the closed-loop utilization of DESs and valuable metals, improve the overall economic benefits of recycling, and promote the industrialization process of DESs-based recycling technology. This review is expected to provide important references for subsequent research and engineering applications in the field of spent LIBs recycling, and contribute to the sustainable development of the new energy industry.