Leaching Mechanisms of Recycling Valuable Metals from Spent Lithium-Ion Batteries by a Malonic Acid-Based Leaching System

Considering the shortage and toxicity of raw materials, recycling cathode materials from spent lithium-ion batteries is currently the most promising measure to realize the green sustainability of cathode materials. Presently, most hydrometallurgical recovery methods and some cathode material synthesis methods are based on the use of acidic solutions. This study addresses the dissolution–chelation mechanism and limitations of the LiNi1/3Mn1/3Co1/3O2 cathode materials in acidic solution, aiming at highlighting the interface reaction mechanism. In this work, malonic acid and hydrogen peroxide were used as the leaching system to conduct efficient green leaching of spent ternary cathode materials. The effects of different reaction parameters on the recovery efficiency of various valuable metal ions were studied by orthogonal and single-factor condition experiments. The results show that under the optimal conditions the leaching efficiency of the lithium ion is 95%, and the leaching efficiencies of Ni, Co, and Mn all reached over 98%. The dissolution mechanism was studied at the macro- and microscales based on the material characterization technology, kinetic studies, and the theoretical calculations of the binding energy of the possible product. Kinetic studies found that the dissolution–chelation process is controlled by chemical reactions or a chemical and diffusion reaction, and calculation results of the activation energy and binding energy show that lithium ions are leached preferentially over other metal ions. In addition, this recovery technology can be effectively used to recycle other spent rechargeable battery materials and may also lay a theoretical foundation for further study on the regeneration and resynthesis of materials.