Effective regeneration of scrapped LiFePO₄ material from spent lithium-ion batteries

Since LiFePO₄ has few other valuable metals except lithium, there are no economic advantages in recovery of scrapped LiFePO₄ by leaching. Therefore, regeneration of scrapped LiFePO₄ is the most reasonable choice. Based on the study of the main cause of the capacity fading of LiFePO₄ (the loss of lithium), traditional regeneration method (solid-phase calcination) and a new process (hydrothermal treatment followed by annealing) are both applied to replenish lithium ions in this work. Compared with solid-phase calcination, hydrothermal treatment can not only make the lithium replenishment more uniform and make the particles have better morphology, but also avoid the side reactions to reduce the formation of impurities. In hydrothermal reaction, the solution dissolves only LiOH and Na₂SO₃. So the waste liquid is easily disposed of and it can’t trigger environmental secondary pollution. In addition, hydrothermal re-lithiation does not require tedious calculation of the amount of lithium to be added. The subsequent annealing can improve the crystallinity, improving the initial and rate capacity. The LiFePO₄ regenerated by solid-phase calcination regained the initial capacity of 135.13 mAh g⁻¹. After hydrothermal reaction at suitable temperatures (150 and 180  °C) followed by annealing, the initial capacity can increase to 144.02 and 141.81 mAh g⁻¹, respectively.