Green and selective recovery of lithium by phosphate based leaching system from spent lithium iron phosphate batteries.

With the increasing market share for lithium iron phosphate (LiFePO4, LFP) batteries, the volume of spent lithium-ion batteries is growing prominently. Current LFP recycling technologies exhibit significant limitations, particularly regarding complex leaching processes and severe secondary environmental pollution. This study addresses these challenges by developing an efficient, economical phosphate-based leaching system that utilizes ammonium dihydrogen phosphate with buffering properties and hydrogen peroxide for selective lithium recovery from spent LFP batteries. Under mild conditions (65 ℃, 20 min), this system achieved exceptional lithium selectivity (100%) and high Li recovery efficiency (95.78%) considering the subsequent regeneration process, while maintaining the iron phosphate structure in the leaching residue. Kinetic modeling and thermodynamic analysis revealed that the leaching process follows a chemical reaction control model with an activation energy of 19.93 kJ/mol. The buffering effect of the phosphate salt system sustained a weakly acidic environment, facilitating selective lithium extraction, while hydrogen peroxide provided the oxidative potential to immobilize iron as insoluble FePO4, thereby inhibiting its dissolution. The recovered lithium carbonate and iron phosphate residue were directly utilized for cathode material regeneration through solid-state synthesis. The regenerated LFP exhibited excellent electrochemical performance, delivering a discharge capacity of 158.72 mAh·g-1 at 0.2C and maintaining 91.33% capacity retention after 400 cycles at 0.5C. Compared to conventional acid leaching methods, this environmentally benign process significantly reduces waste generation and processing steps, offering a promising approach for sustainable recycling of spent LiFePO4 batteries.