Trends of sustainable recycling technology for lithium-ion batteries: Metal recovery from conventional metallurgical processes to innovative direct recycling

The remarkable market growth of lithium-ion batteries (LIBs) for various applications has been witnessed in the past two decades. However, as a retirement wave of more and more LIBs approaches, the disposed end-of-life batteries represent a growing hazard to ecosystem and human health. Recycling valuable metals from those spent LIBs still remain challenging because the current conventional metallurgical recycling processes involve the emission of toxic gas and waste chemicals as well as intensive energy consumption. These processes are not considered as green recycling approaches that contradict with the principles of carbon neutrality and circular economy embraced by the world. Hence, implementing green and sustainable recycling technologies of spent LIBs, especially for cathode materials, is an urgent need. This review provides a comprehensive understanding and critical evaluation of traditional pyrometallurgy, hydrometallurgy, and state-of-the-art direct recycling for recovering valuable metal materials from the spent LIB cathode. The fundamentals, methods, efficiencies, and feasibility of the three recycling approaches are also assessed. In addition, the recent progress for green innovation of hydrometallurgical and direct recycling processes as well as the potential research tendency for spent LIBs are discussed.