Sustainable Recycling of Electrode Materials in Spent Li-Ion Batteries through Direct Regeneration Processes

The prevalence of electric vehicles (EVs) globally could generate a huge number of spent Li-ion batteries (LIBs) as they reach their end of life. It is expected that by 2030, 11 million metric tons of EOL LIBs will be generated cumulatively, with annual waste flows of EV batteries reaching 34,000 t by 2040. Recycling spent LIBs in a sustainable and effective manner is a matter of utmost importance. Conventional recycling strategies such as pyrometallurgy and hydrometallurgy decompose the crystal structures of value-added electrode materials to element levels, presenting fatal drawbacks in high greenhouse gas emissions, cost, and energy consumption. The burgeoning direct recycling processes provide viable options to rejuvenate LIB compounds without chemical change, thus retaining their original composition as well as the embedded energy. Relithiation and defect restoration are the critical steps for electrode regeneration, which determine the performance of recovered material. Here, the authors provide a detailed discussion and analysis on different regeneration methods for LIB electrodes based on their degradation mechanisms. The advancements of direct recycling among other recycling technologies are highlighted through discussions of its process benefits. Physical pretreatments including deactivation, disassembly, and black mass separation are introduced. Perspectives toward scaled applications of direct recycling are also demonstrated on the basis of developing trends of future LIBs.