Recovery and regeneration of anode graphite from spent lithium-ion batteries through deep eutectic solvent treatment: Structural characteristics, electrochemical performance and regeneration mechanism

Recovery of graphite from spent lithium-ion batteries (LIBs) as new anode materials in the LIBs after regeneration can not only promote the recycling of spent LIBs, but also help to alleviate its environmental risks. However, the removal of the impurities in spent graphite is unsatisfying and its electrochemical performance need to be further improved when using conventional regeneration methods (such as acid treatment). Herein, we proposed a novel deep eutectic solvent (DES) leaching method to recover and regenerate waste graphite from spent LIBs under mild condition. The result showed that DES leaching could not only effectively remove the impurities in spent graphite, but also restore its crystal structure and morphology. The regenerated graphite obtained by DES treatment (DRG) exhibited a high specific capacity of 449.4 mAh/g for the first cycle at 0.1C and 285.4 mA h/g even after 500 cycles at 1C. In addition, the retention rate and coulombic efficiency of DRG were as high as 96.0 % and 100 %, respectively. These results demonstrated the excellent electrochemical performance of DRG, which was even comparable to that of commercial graphite. The regeneration mechanism of the proposed method was also elucidated. The organic binder was dissolved in DES by forming hydrogen bonds (OH…F and CH…Cl−). The Li coordination complex formed between SEI film and DES contributed to the dissolution of SEI film, and the residual electrolytes were removed based on the similarity-intermiscibility theory. This study provides a facile and green method to accomplish the closed-loop utilization of spent graphite in spent LIBs.