Inherent fluorine impurity enhances the regeneration of highly degraded layered cathodes with suppressed lattice oxygen escape

To face the large–scale retirement of lithium–ion batteries (LIBs), direct regeneration of spent NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) cathode can effectively alleviate the current resource and environmental pressures. During the recycling process, the binder polyvinylidene fluoride (PVDF) inevitably becomes an inherent impurity in the active material. Whether the inherent impurity can assist the regeneration of spent NCM or not is becoming a focus of attentions. Hereby, a closed–loop direct regeneration strategy that transforms the inherent PVDF impurity into a F dopant is proposed, and a LiNO 3 –LiOH eutectic molten system is utilized to repair the elemental loss and structural defects in highly degraded NCM622 cathode while achieving F doping. It is found that the fluorine element is uniformly doped into both the surface and bulk phases of the whole material. The F–containing regenerated NCM cathode (R–NCM622–F) shows a stable layered structure with markedly suppressed lattice oxygen escape, as substantiated by the experimental analysis and theoretical calculation. As a result, the obtained R–NCM622–F exhibits a satisfactory repaired specific capacity of 169.6 mAh g −1 and excellent cycling stability, which retains 85.8 % of its initial capacity after 200 cycles. Meanwhile, it can deliver a considerable capacity of 120mAh g −1 even at a high rate of 5C. Clearly, our regeneration strategy obviates the necessity for intricate pretreatments, and instead employs the inherent PVDF impurity to achieve the direct regeneration process, thereby offering a promising avenue to the large–scale direct regeneration of layered cathodes.