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

Abstract

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.