Extraction of polyvinylidene fluoride binder materials for used secondary batteries using supercritical CO2 for an effective battery recycling process

In this study, a polyvinylidene fluoride (PVDF) binder material for secondary batteries was removed using a supercritical CO2 extraction process instead of conventional extraction processes such as leaching and pyrolysis. To determine the optimal process conditions, the phase behavior of the binder in CO2 was studied by measuring the pressure and temperature before the supercritical CO2 extraction. To design an effective extraction process, the extraction time, temperature, and pressure were studied under various experimental conditions using a supercritical extraction system. Various organic cosolvents were used in the experiment to improve the extraction efficiency. According to the experimental result, the optimal extraction conditions were determined to 353.2 K, 10 MPa, and 20 min with dimethylformamide (DMF) cosolvent. Under these process conditions, the removal rate of the binder was 98.8 %. However, there was a significant difference in cell performance such as initial discharge capacity and cycling stability depending on the extraction solvent. Specifically, cycling stability improved in the order of using DMF, NMP, DMSO, and DMAc. The extracted binder material was analyzed by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) to compare the raw and processed materials and evaluate the reusability of the binder material.