The Fischer-Lactonization-Driven Mechanism for Ultra-Efficient Recycling of Spent Lithium-Ion Batteries.

Hydrometallurgy remains a major challenge to simplify its complex separation and precipitation processes for spent lithium-ion batteries (LIBs). Herein, we propose a Fischer-lactonization-driven mechanism 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 lactonized gel. The leaching rates of Li, Ni, Co and Mn are 99.3, 99.1, 99.5 and 99.2 %, respectively. The regenerated monocrystalline LiNiCoMnO (NCM523) has a uniform particle size distribution and complete lamellar structure, with a capacity retention rate of 70.6 % after 250 cycles at 0.5 C. The mechanism 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.