Direct Regeneration of Spent LiFePO₄ Cathode Material by a Green and Efficient One-Step Hydrothermal Method

The environmentally friendly and low-cost recycling of spent LiFePO4 (LFP) cathode material has become an urgent problem. Herein, a green and effective one-step hydrothermal approach was proposed for the direct regeneration of spent LFP. LFP will lose part of its lithium and convert into FePO4 (FP) during long-term cycles. Thus, a supplement of lost lithium is essential to regenerate spent LFP, and this is thermodynamically feasible to achieve under hydrothermal conditions. The hydrothermal conditions of temperature, Li+ concentration, and reductant dosage were investigated. It was found that enhancement of hydrothermal conditions was beneficial to supplementing lithium, correspondingly improving the electrochemical performance. Under the hydrothermal conditions of 200 °C for 3 h, 12 g L–1 of Li+, L/S = 6 mL g–1, and 1.0 mL of reductant (for every 5 g of spent LFP), the regenerated LFP displayed excellent discharge capacities of 146.2 mAh g–1 at 0.2 C, 141.9 mAh g–1 at 1 C, and 128.2 mAh g–1 at 5 C. Additionally, the capacity retention reached up to 98.6% after 200 cycles at 1 C. This regeneration method has been demonstrated to be of good economic benefit and energy savings, which will provide technological support for the sustainable development of the LIBs industry.