Abstract: The extensive application of lithium-ion batteries (LIBs) in recent years has led to a sharp increase in the volume of spent batteries, giving rise to pressing global challenges related to resource scarcity and environmental impact. Taking 2024 as an example, global LIBs production has exceeded 1,850 GWh. Projections indicate that, driven by carbon neutrality commitments, emission peak targets, and the expansion of the new energy vehicle market, global LIBs production may surpass 6,080.4 GWh by 2030. As these large-scale deployments reach their end-of-life, the volume of retired batteries is rising dramatically. It is estimated that the total amount of spent LIBs in China will reach 2.312 million tons by 2026, while the global scale of decommissioned LIBs is expected to exceed 11 million tons by 2030. However, the current global annual recycling capacity for spent LIBs stands at only about 2 million tons. Consequently, there is an urgent need to develop efficient and environmentally benign battery recycling methodologies. Recycling technologies for spent LIBs primarily fall into two categories: pyrometallurgy and hydrometallurgy. Pyrometallurgy often suffers from metal loss through volatilization, high energy consumption, elevated carbon emissions, and associated environmental issues. Compared to pyrometallurgy, hydrometallurgy offers advantages in higher recovery rates and reduced environmental footprint, establishing itself as the most commonly employed and promising method for recovering valuable metals from spent LIBs. This review systematically summarizes research progress in acid leaching technologies for recovering high-value metals from the cathode materials of spent LIBs, with a particular focus on recent advancements in green leaching strategies and metal separation/purification techniques. Beyond traditional inorganic and organic acid leaching systems, this article highlights the emerging green technology of deep eutectic solvent (DES) leaching, discussing its potential for efficient metal extraction and minimized environmental pollution. Furthermore, the review delineates principal methods for metal separation and recovery from leachates, including solvent extraction, chemical precipitation, sol-gel processes, ion exchange, and electrochemical deposition, providing a comparative analysis of the strengths and limitations of different combined process routes. Finally, this article outlines future research directions, proposing the further development of green, low-cost multi-component leaching systems, promoting the circular use of leaching agents, and advancing integrated, short-flow metal recovery processes to enhance the economic viability and environmental sustainability of spent LIB recycling. Through systematic optimization of the acid leaching stage and subsequent metal recovery steps, it is anticipated that the LIB recycling industry will advance towards more sustainable, efficient, and scalable development.