Recovery of spent LiFePO4: Unveiling iron migration mechanism towards selective lithium extraction

Selective leaching recovery for spent LiFePO 4 (LFP) has garnered significant attention owing to its advantages of low-cost, high-efficiency and eco-friendliness. Wherein, the separation effect of Li and Fe is particularly crucial. While previous studies have yielded effective Li-Fe separations experimentally, the migration behavior of Fe during the selective leaching process remains unexplored methodically. Herein, this work systematically investigated the selective leaching characteristics and regeneration behavior of spent LFP in the H 2 O 2 -H 2 SO 4 system. Particularly, for the first time, a migration mechanism of Fe involving precipitation-dissolution and hydrolysis equilibria has been proposed. Specifically, the proportion of Fe that forms precipitate or exists in the filtrate is dependent on the real-time pH value. The result indicates that at an optimized pH of 3, an effective separation of Li (>98 %) and Fe (<0.1 %) is achieved. Additionally, FePO 4 ·2H 2 O was recovered from the residue through a recirculated process and employed to resynthesize LFP/C, which exhibits excellent specific discharge capacity of 158 mAh·g −1 at 0.1 C and maintains a capacity retention ratio of 99 % after 300 cycles at 2 C. The proposed mechanism is expected to guide highly selective extraction of Li, and the recovery process avoids excessive reagent consumption and secondary pollutions in principle.