Application of response surface methodology and thermogravimetric-Fourier transform infrared spectroscopy on the recycling of graphite from spent lithium-ion batteries by ultrasonic-assisted water leaching and pyrolysis treatment

Recycling and regenerating graphite from spent lithium-ion batteries (SLIBs) is crucial for its environmental and economic benefits. This study employs ultrasonic-assisted water leaching and pyrolysis treatment to effectively remove impurities from spent graphite (SG) in SLIBs. The effects of independent variables in the leaching process are methodically investigated using the response surface methodology (RSM). Furthermore, the significance of the models is assessed using analysis of variance (ANOVA). In addition, the gaseous products generated from the pyrolysis of SG at various temperatures are analyzed using thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR). The experimental results from the leaching process align well with the RSM models, as evidenced by low p-values and high R2 values. Under optimal conditions obtained by RSM, the leaching efficiencies for Li and Fe have reached 97.62 % and 37.23 %, respectively. Moreover, based on the TG-FTIR results,most impurities in the SG are effectively decomposed after 30 min at 500 degrees C. Finally, the purified graphite (PG) exhibits enhanced electrochemical performance after leaching and pyrolysis. It achieves an average initial coulombic efficiency of 83.03 % and a stable specific capacity of approximately 340.0 mAh g-1 at a rate of 0.1 C. These findings suggest a feasible approach for impurity elimination of graphite anode from SLIBs.