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 - Fe-2(SO4)(3) to recover lithium from LiFePO4 are proposed. The method-1 is theoretical-molar Fe-2(SO4)(3) Fe-2(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 Fe-2(SO4)(3) is decreased by two thirds Fe-2(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 Fe-2(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.