Synergistic leaching of spent LiNi_xCo_yMn_zO₂ cathode materials using tannic acid and gluconic acid: A green approach for valuable metals recovery

The recycling of spent lithium-ion batteries (LIBs) has attracted increasing attention due to the scarcity of critical metals and environmental concerns. In this study, a novel green leaching system combining tannic acid and gluconic acid was developed for the efficient recovery of valuable metals (Li, Ni, Co, and Mn) from spent LiNi _x Co _y Mn _z O₂ (NCM) cathode materials. Both organic acids possess hydroxyl and carboxyl groups, enabling their synergistic roles in the leaching process through combined acidolysis, reduction, and complexation. The leaching parameters, including gluconic acid (GA) volume fraction, tannic acid (TA) dosage, liquid-to-solid ratio, temperature, and time, were systematically optimized. Under the optimal conditions, the leaching efficiencies of Li, Ni, Co, and Mn all reached 99.9%. The synergistic mechanism was elucidated through a combination of characterization techniques, revealing that the cooperative interplay of acidolysis, reduction, and complexation between the two acids is responsible for the remarkable leaching performance. This study not only provides a sustainable and efficient approach for metal recovery from spent NCM materials but also offers mechanistic insights into the synergistic interactions between organic acids in hydrometallurgical processes, contributing to the development of green recycling technologies for spent LIBs.