Dissolution Mechanisms of LiNi_1/3Mn_1/3Co_1/3O₂ Positive Electrode Material from Lithium-Ion Batteries in Acid Solution

The sustainability through the energy and environmental costs involve the development of new cathode materials, considering the material abundance, the toxicity, and the end of life. Currently, some synthesis methods of new cathode materials and a large majority of recycling processes are based on the use of acidic solutions. This study addresses the mechanistic and limiting aspects on the dissolution of the layered LiNi_1/3Mn_1/3Co_1/3O₂ oxide in acidic solution. The results show a dissolution of the active cathode material in two steps, which leads to the formation of a well-defined core-shell structure inducing an enrichment in manganese on the particle surface. The crucial role of lithium extraction is discussed and considered as the source of a "self-regulating" dissolution process. The delithiation involves a cumulative charge compensation by the cationic and anionic redox reactions. The electrons generated from the compensation of charge conduct to the dissolution by the protons. The delithiation and its implications on the side reactions, by the modification of the potential, explain the structural and compositional evolutions observed toward a composite material MnO₂·Li _xMO₂ (M = Ni, Mn, and Co). The study shows a clear way to produce new cathode materials and recover transition metals from Li-ion batteries by hydrometallurgical processes.