Revealing role of oxidation in recycling spent lithium iron phosphate through acid leaching

Abstract The efficient recycling of spent lithium iron phosphate (LiFePO 4 , also referred to as LFP) should convert Fe (II) to Fe (III), which is key to the extraction of Li and separation of Fe and is not well understood. Herein, we systematically study the oxidation of LiFePO 4 in the air and in the solution containing oxidants such as H 2 O 2 and the effect of oxidation on the leaching behaviors of LFP. In the air, O 2 breaks down the LFP olivine structure at 550 °C for 1 h by oxidizing Fe (II) to Fe (III) in terms of converting LFP to Li 3 Fe 2 (PO 4 ) 3 and Fe 2 O 3 . After that, Li is leached in 0.5 M sulfuric acid solution and is further recycled as Li 3 PO 4 with a Li recovery efficiency of 97.48%. Meanwhile, Fe is recovered as FePO 4 and Fe 2 O 3 . Compared with H 2 SO 4 –H 2 O 2 , the air oxidation saves H 2 O 2 but increases the leaching efficiency of Fe and H 2 SO 4 consumption. The discrepancy of Fe leaching efficiency can be attributed to the different leaching mechanisms involving the solid‐to‐solid and solid‐to‐liquid‐to‐solid conversions. Furthermore, the results of the Everbatt model analysis show that the air roasting‐H 2 SO 4 leaching method has low emission and potentially high income, which is simple and safe. Overall, this work will deepen the understanding of acid leaching of LFP and favorably stimulate the maturation of the LFP recycling technique.