Upcycling of Spent High-Nickel Layered Cathodes: A Mechanism-Guided Framework for Single-Crystal Structural Healing

The escalating demand for electric transportation and renewable energy necessitates sustainable recycling of spent lithium-ion batteries, particularly nickel-rich layered oxide cathodes. However, conventional metallurgical methods suffer from high energy consumption and product downcycling, while current direct recycling is severely limited by complex multiscale degradation mechanisms. Addressing the critical mismatch between recovered legacy materials and the stringent requirements for high-performance cathodes, this review advocates a paradigm shift from simple element recovery to functional structural regeneration via upcycling protocols. We establish a mechanism-guided framework that elucidate degradation pathway to targeted rejuvenation strategies. Central to this approach is the conversion of degraded polycrystalline particles into single-crystal architectures. This strategy fundamentally addresses intergranular cracking and heals lattice strain, enabling the restored materials to rival or even surpass the stability of pristine counterparts. Finally, the review highlights critical prospects for the field, including impurity tolerance quantification, AI-integrated operando characterization, and the need for standardized Life Cycle Assessment (LCA) and Techno-Economic Analysis (TEA), aiming to chart a viable protocol for the next-generation closed-loop battery supply chain.