Regeneration of LiNixCoyMnzO2 cathode materials from spent lithium-ion batteries: A review

The large-scale implementation of electric vehicles worldwide has driven the further expansion of lithium-ion battery (LIB) production, especially those employing the layered LiNixCoyMnzO2 cathode materials with excellent electrochemical performance. However, since LIBs have a limited lifespan, a wave of used cells containing spent LiNixCoyMnzO2 cathode materials can be expected in the near future. Regeneration of spent materials is a vital component in the recycling of valuable metals for the sustainable development of the LIB industry. This review focuses on the recently developed regeneration methods of spent LiNixCoyMnzO2 cathode materials. First, the degradation mechanisms of layered LiNixCoyMnzO2 materials are discussed. These mechanisms could serve as the guidelines for the design of many highly efficient regeneration strategies. Furthermore, we discuss the emerging direct regeneration approach enabled by the relithiation of spent materials using techniques such as molten salt, hydrothermal treatment and Li redox mediator. Finally, indirect regeneration processes are summarized, including acid and ammonia leaching, leaching kinetics, re-synthesis from leachates via co-precipitation and sol-gel methods, as well as the removal of impurities by co-extraction. By summarizing the achievements made on the regeneration of LiNixCoyMnzO2 materials, this review also identifies associated challenges and provides insights for further developments toward a greener and more effective recycling of LiNixCoyMnzO2 materials.