Theoretical-molar Fe³⁺ recovering lithium from spent LiFePO₄ batteries: an acid-free, efficient, and selective process

In spent lithium iron phosphate batteries, lithium has a considerable recovery value but its content is quite low, thus a low-cost and efficient recycling process has become a challenging research topic. In this paper, two methods about using the non-oxidizing inorganic iron salt - Fe₂(SO₄)₃ to recover lithium from LiFePO₄ are proposed. The method-1 is theoretical-molar Fe₂(SO₄)₃ (Fe₂(SO₄)₃ : LiFePO₄ =1:2) dosage is added and more than 97% of lithium can be leached in just 30 min even under a pretty high solid-liquid ratio of 500 g/L. Spectrophotometry provides the evidence of Fe²⁺/Fe³⁺ substitution in the leaching process. In the method-2, the generated Fe²⁺ originating from LiFePO₄ is fully utilized with the addition of H₂O₂, and the dosage of Fe₂(SO₄)₃ is decreased by two thirds (Fe₂(SO₄)₃ : LiFePO₄ =1:6). Several sulphates (CuSO₄, NiSO₄, MgSO₄) are employed to explore the leaching mechanism. All the results reveal that the reaction of Fe³⁺ substituting Fe²⁺ has a powerful driving force. In addition, these two leaching processes simultaneously present superior selectivity for the impurities. The Fe₂(SO₄)₃ in two methods does not cause pollution and is easily regenerated by adding H₂SO₄. The proposed rapid, efficient and selective leaching thought would be a competitive candidate for recycling spent LiFePO₄ batteries.