Review and Perspectives on Direct Regeneration of Spent Ternary Cathode Materials Based on Failure Mechanisms

Currently, the rising demand for lithium-ion batteries (LIBs) in energy storage systems is leading to a significant increase in the number of discarded lithium-ion batteries. Given the limited availability of strategic metal resources, the considerable environmental harm caused, and the intrinsic value of waste lithium-ion batteries, recycling these batteries is of paramount importance. Inadequate disposal of waste lithium-ion batteries (LIBs) can severely impact resource efficiency and hinder sustainable development for humanity. There are currently three mainstream recycling methods, namely pyrometallurgy, hydrometallurgy, and direct regeneration technology. Direct regeneration has attracted much attention due to its significant environmental and economic advantages. The direct regeneration method is a technique for restoring electrochemical performance by fixing defects in waste materials while preserving the original structure of the materials. Therefore, the advancement of direct regeneration technology largely relies on understanding the failure mechanism of waste lithium ions. However, direct repair is an emerging technology that faces numerous challenges, including limited research on targeted repair methods based on the failure mechanisms of batteries. In the realm of lithium-ion battery cathodes, layered ternary cathode materials NCM/NCA have garnered significant attention because of their high reversible capacity, high operating voltage, and low cost. This review offers a thorough and detailed examination of the degradation mechanisms and defect types in ternary cathode materials. Based on this understanding, it outlines the principles and methods for directly repairing failed ternary materials. By examining the mechanisms, benefits, and drawbacks of different direct regeneration techniques, along with the relationship between battery failure mechanisms and direct regeneration, we strive to choose specific repair methods tailored to the actual failure conditions of retired NCM/NCA batteries during maintenance.