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

Abstract

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.

Dual-Function Regeneration of Waste Lithium Cobalt Oxide for Stable High Voltage Cycle Performance

“…The change of structure was analyzed by X-ray diffraction (XRD) and is shown in Figure . Results show that the patterns are basically consistent with the standard pattern of LiCoO 2 (PDF #75-0532), and the materials both belong to the corresponding hexagonal R 3̅ m structure . However, the crystallinity of W-LCO is poor, and there is a Co 3 O 4 peak around 28.58°.…”

“…Results show that the patterns are basically consistent with the standard pattern of LiCoO 2 (PDF #75-0532), and the materials both belong to the corresponding hexagonal R3̅ m structure. 22 However, the crystallinity of W-LCO is poor, and there is a Co 3 O 4 peak around 28.58°. Co 3 O 4 may be caused by the irreversible phase transition of LiCoO 2 during the cycle.…”

Advances and Challenges on Recycling the Electrode and Electrolyte Materials in Spent Lithium-Ion Batteries

“…Many researches have been done to reprepare new cathode materials. The main repreparation methods can typically be classified in four types: hydrothermal method, [107][108][109] solid phase method, [110][111][112] coprecipitation, [113][114][115] and sol-gel. [116][117][118] Hydrothermal method uses a thermal treatment process to replenish lost lithium resources in cathode materials.…”

“…Wang et al [119] adopted an ionothermal relithiation to directly regenerate NCM cathodes with ionic liquid (IL)as solvent and al. [107] reported a hydrothermal method for spent LiFePO 4 regeneration with N 2 H 4 •H 2 O as both reductant and pH buffer (Figure 7a). The investigation shows that not only the temperature but also the reductant dosage is beneficial to the relithiation.…”

“…Figure7. Flowchart of regeneration process for cathode materials: (a) hydrothermal method [107]. Copyright 2020, American Chemical Society.…”