Upcycling spent cathode materials from Li-ion batteries to precursors: Challenges and opportunities

Today's rapid increase in lithium-ion battery (LIBs) applications exacerbates a voluminous rise of spent LIBs. Furthermore, manufacturing LIB cathode materials demands valuable metals depleting from the earth crust. Efficient routes are urgently needed to address these problems for upcycling cathode materials from spent LIBs into precursors for manufacturing new LIB cathode materials. Hydrometallurgy is a popular method for extracting metal from spent LIB cathode materials, wherein precipitation processes serve as the foundation for obtaining metal salts. However, the resulting precipitate metal salts are often inferior in yield and quality, limiting their use as precursors for resynthesizing new LIB cathode materials. This review is dedicated to untangling the individual challenges in the precipitation processes, identifying the root causes, and their effects on the quality and yield of the precursors. Based on the problem cause-effect correlation, enhancement strategies, research design guidelines, and future perspectives are highlighted to improve the precipitation processes and the precursor quality and yield for LIB cathode material resynthesis.