Stepwise Recovery of Valuable Metals from Spent Lithium-Ion Batteries Through In Situ Thermal Reduction and Selective Leaching

The sustainable recycling of valuable metals from spent lithium-ion batteries (LIBs) is imperative for closing the resource loop. This study presents an integrated strategy for the stepwise recovery of metals from spent cathode sheets by in situ thermal reduction and selective leaching. The in situ thermal reduction converted the cathode material into a mixture of Li2CO3, LiAlO2, Ni, Co, NiO, and CoO while simultaneously liberating the cathode materials from the Al current collector through binder removal. A combined process of water leaching, wet sieving, and filtration successfully achieved the separation and enrichment of Li-rich aqueous solution (near 60% Li), Al-rich coarse fraction (over 87% Al), and fine powder enriched with transition metals (over 90% of Ni, Co, and Mn). The pyrolysis gases released from binder decomposition were the key driver for forming Li2CO3, whereas the concurrent generation of LiF and LiAlO2 limited direct water leaching efficiency. An alkaline leaching step was therefore introduced to co-extract Al and the associated Li from LiAlO2, followed by an acid leaching step that recovered over 96% of the transition metals from the treated residue without external reductants. Complete mass balance analysis shows that the integrated process achieved overall recoveries of 91.86% for Li, 91.93% for Ni, 92.23% for Co, and 92.61% for Mn from all the combined leachate streams. Consequently, this work provides a reagent-saving, stepwise hydrometallurgical process for the comprehensive recycling of valuable metals from spent LIBs.