Resourcing phosphorus iron slag for lithium iron phosphate cathode material

Phosphorus iron slag (PIS), a solid waste containing over 80% phosphorus and iron, is generated during yellow phosphorus production and poses significant environmental risks due to open stacking. In this study, we developed a novel recycling method to directly convert PIS into lithium iron phosphate (LFP) for battery applications. By reducing the particle size of PIS to approximately 25 μm, we achieved a leaching rate of up to 96.15% through acid leaching, which followed a surface chemical mechanism. The leached solution was adjusted for the Fe/P molar ratio and treated with CTAB to precipitate pure FePO4 precursor with uniform particle size. This precursor was then sintered with glucose and lithium carbonate to synthesize LFP. The recycled LFP exhibited an initial capacity of 146.6 mAh g-1 at 1 C in aprotic lithium-ion batteries (LIBs), retaining 90.51% of its capacity after 150 cycles. In aqueous LIBs, the recycled LFP delivered a capacity of 113.2 mAh g-1 at 1 C, with 82.55% capacity retention after 150 cycles and near-100% Coulombic efficiency. This approach not only demonstrates economic and environmental benefits by recycling PIS but also provides an alternative pathway to reduce LIB production costs.