Upcycling of lithium-depleted lithium-ion battery recycling residues: Potential as an alternative filler for performance enhancement of asphalt binders

This study focuses on lithium-depleted lithium-ion battery recycling residue waste (LW) and investigates its feasibility as an alternative filler for asphalt binders. The objective is to address the challenges associated with the inefficient recovery and utilization of lithium-depleted residues arising from their limited economic value, while simultaneously enhancing asphalt performance and enabling the value-added utilization of battery recycling waste. LW, a lithium-depleted black mass residue primarily composed of iron phosphate and graphite, was incorporated into both a base asphalt binder and a styrene–butadiene–styrene (SBS)-modified binder at dosages of 3 wt% and 6 wt%. Rheological behavior was characterized using dynamic shear rheometer (DSR) master curves and phase angle analysis, while thermal properties were evaluated via differential scanning calorimetry (DSC). Tests were conducted under unaged, pressure aging vessel (PAV)-aged, and double-PAV-aged conditions. The results indicate that LW has a negligible effect on initial stiffness and viscoelastic balance in the unaged state. However, LW markedly suppresses aging-induced stiffening across the entire frequency spectrum, leading to convergence of complex modulus master curves and a substantial reduction in the aging hardening. In parallel, LW significantly lowers the glass transition temperature and enhances resistance to progressive aging. Therefore, both the low-temperature performance and the aging resistance were improved. It is noteworthy that the performance improvements are largely insensitive to the content of LW, which suggests that a small LW addition is sufficient to achieve the desired improvement. The findings demonstrate that LW is a promising sustainable alternative filler capable of improving aging resistance and low-temperature performance in both base and SBS-modified asphalt binders, while offering a scalable pathway for valorization of lithium-ion battery recycling residues.