Resourcing phosphorus iron slag for lithium iron phosphate cathode material

• Revealed the size effect in leaching phosphorus iron slag (PIS) and achieved a leaching rate of up to 96.15%. • The recycled lithium iron phosphate (LFP) exhibited competitive performance to the commercial LFP. • Recycling PIS for aprotic and aqueous lithium-ion batteries offers significant economic and environmental advantages. 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 FePO 4 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.