Hydrometallurgy remains a major challenge to simplify its complex separation and precipitation processes for spent lithium-ion batteries (LIBs). Herein,we propose a Fischer-lactonisation-drivenmechanism for the cascade reaction of leaching and chelation of spent LIBs. Citric acid undergoes a two-step dissociation of the carboxylic acid (-COOH) and complexes with the leached metal ion, while the residual -COOH is attacked by H protons to form a protonated carboxyl ion (-COO^-). Subsequently, the lone pair of electrons in the hydroxyl of the same molecule attack the carbon atom in -COO^- to facilitate ester bonding, leading to the formation of a lactonizedgel.The leaching rates of Li, Ni, Co and Mn are 99.3, 99.1, 99.5 and 99.2%, respectively.The regeneratedmonocrystallineLiNi0.5Co0.2Mn0.3O2(NCM523)hasa uniform particle size distribution and complete lamellar structure,with a capacity retention rate of 70.6% after 250 cycles at 0.5 C. Themechanism achieves a one-step chelation reaction, and the energy consumption and carbon emissions are only 26% and 44%, respectively, of that of the conventional hydrometallurgical.The strategy achieves a double breakthrough in simplifying the process and improving environmental friendliness, offering a sustainable approach to the re-utilization of spent LIBs.