Abstract: Worldwide demands for green energy have driven the ever-growing popularity of electric vehicles, resulting in demands for a million tons of lithium-ion batteries (LIBs). Such exigency will not only outstrip the current reserves of critical metals, such as Li, Co, Ni, and Mn, which are essential for LIB fabrication, but also necessitate the methods to properly, safely, and sustainably handle spent LIBs. Current LIB recycling infrastructure uses pyrometallurgical or hydrometallurgical methods and mainly focuses on cobalt recovery to maximize economic benefits. Despite being commercialized, these two methods are either energy-intensive or highly complicated, and their long-term economic feasibility is still uncertain, as the market trend is shifting towards cobalt-poor or even cobalt-free chemistry. Alternative non-destructive methods, including direct recycling and upcycling, have attracted much interest. Direct recycling, which is a non-destructive method, allows spent cathodes to be directly regenerated into new active materials for reuse, while upcycling, as an upgraded direct recycling method, transforms degraded cathode materials into materials with a better performance or applicability in other fields. This review mainly focuses on recent advances in techniques including pyro- and hydrometallurgy, direct recycling, and upcycling.

Key words: Hydrometallurgy, Pyrometallurgy, Direct recycling, Upcycling, Spent lithium-ion batteries