Toward Single‐Crystal Upcycling of Degraded Lithium‐Ion Battery Cathodes

ABSTRACT Researchers on degraded lithium ion batteries are increasingly focusing on direct recycling, a more sustainable approach than pyrometallurgy and hydrometallurgy. More precisely, the upcycling approach has attracted widespread attention. However, beyond economic advantages, the sustainability of these upcycling strategies, including their environmental footprint and long‐term viability, is equally critical for achieving truly circular battery systems. This review first provides a multi‐level, multi‐scale overview of the degradation mechanisms of polycrystalline cathodes and the advantages of single‐crystal cathodes. It then focuses on strategies for regenerating single‐crystal cathodes, covering solid‐state sintering, and molten‐salt‐assisted and hybrid‐assisted upcycling strategies. Additionally, the review explores the advantages of single‐crystal cathodes and strategies for optimizing their single‐crystallization from the perspectives of surface modification, structural optimization, defect engineering, kinetics, and environmental impact. Finally, this article highlights the significant competitive edge of single‐crystal cathodes in lithium‐ion battery recycling and proposes the following: (i) classify and grade degraded cathodes prior to recycling; (ii) establish a database for degraded cathodes and apply machine learning; (iii) develop nickel‐rich, cobalt‐poor single‐crystal cathodes; and (iv) quantify the carbon and water footprints during the recycling process.