From Spent Batteries to Green Hydrogen: Catalytic Upcycling of Lithium‐Ion Battery Cathodes for Water Electrolysis

ABSTRACT The accelerating global “dual‐carbon” transition and the rapid proliferation of electric vehicles are driving an unprecedented surge in spent lithium‐ion batteries (LIBs), with the first major retirement peak expected around 2030. Cathode materials form a pivotal bridge between urban mining and green‐hydrogen technologies, coupling environmental risks with the strategic importance of critical metals. This review delivers a comprehensive overview of the recycling and upcycling landscape for the three dominant cathode families—LiCoO 2 , LiNi x Co y Mn 1‐x‐y O 2 , and LiFePO 4 . We outline the compositional and structural features of these materials, evaluate pretreatment protocols, and critically compare pyrometallurgical, hydrometallurgical, and direct‐regeneration strategies. We then highlight how multiscale structure–activity correlations guide the transformation of regenerated cathodes into high‐performance electrocatalysts, with emphasis on defect engineering, electronic‐structure modulation, interfacial coupling, and the assembly of conductive networks to accelerate both hydrogen‐ and oxygen‐evolution pathways. Finally, we propose a forward‐looking design framework that integrates atomic‐site dynamics, multimetallic synergy, and process‐environment co‐optimization, while underscoring emerging opportunities in machine‐learning‐guided inverse design, operando mechanistic mapping, and device‐level implementation. This review provides a conceptual blueprint for integrating battery recycling with green‐hydrogen production in a closed‐loop materials ecosystem.