Research progress on resource regeneration of spent ternary cathode materials

In recent years, with the gradual expansion of the global market for new energy vehicles, the supply and demand of lithium-ion batteries (LIBs) as a source of energy have been increasing, which directly promotes the significant increase in the number of used LIBs. Among them, ternary LIBs have been widely used because of their high specific capacity and excellent multiplying performance, which has aroused people’s concerns about their proper disposal. On the one hand, ternary LIBs contain rich nonferrous metals, such as lithium, nickel, cobalt, and manganese, with high recovery values. On the other hand, spent ternary LIBs contain a large number of toxic electrolytes and heavy metals, which will cause environmental pollution and damage human health if not handled properly. Therefore, research on the recycling and regeneration of spent ternary LIBs has been receiving considerable attention. Given the principles of low energy consumption, “green” recovery, and high recovery rate, this study briefly introduces the main failure causes of cathode materials for ternary LIBs and discusses the application scope and the advantages and disadvantages of traditional pyrometallurgy (such as chemical reduction and salinization roasting) and hydrometallurgical leaching processes (such as acid, alkali, and biological leaching). This review creatively summarizes the research progress on regeneration after hydrometallurgical leaching (such as coprecipitation and sol–gel methods) and direct regeneration (such as high-temperature solid-phase method, solvothermal treatment, and molten salt method) of spent ternary LIBs in recent years and analyzes the advantages and disadvantages of various regeneration technologies. Notably, compared with traditional pyrometallurgy and hydrometallurgy, the process of regeneration after hydrometallurgical leaching and direct regeneration considerably reduces the complexity of the process flow, maximizes the comprehensive utilization rate of nonferrous metals, and realizes the closed-loop recovery route of spent LIB cathode. Based on this, the innovative strategy of upgrading the cathode material of regenerated ternary LIBs through ion doping and surface coating modification, which effectively improved the poor thermal stability, short cycling, and low rate performance of ternary LIBs caused by high nickel content, was particularly discussed. Finally, from the perspective of recycling methods, multiple modification strategies, and mechanism research, the future development of recycling technology for spent ternary LIBs is proposed. This study aims to provide some references and suggestions for the improvement of the spent LIB recycling system and establish a closed-cycle recycling system for the production and recycling of spent LIBs.