Waste Organic Compounds Thermal Treatment and Valuable Cathode Materials Recovery from Spent LiFePO4 Batteries by Vacuum Pyrolysis

This study investigated the gaseous products evolution behaviors and the recovery performance of cathode materials from spent LiFePO4 batteries by vacuum pyrolysis. The thermogravimetric-differential scanning calorimetry analysis coupled with electron ionization mass spectrometry (TG-DSC-EI-MS) results indicated that inorganic gases (H2O, CO, CO2), alkane gases (CH4, C2H4, C2H6, CH3OH, C3H6, C3H4O3, C4H8O3), and fluoride-containing gases (HF, OPF3, C2H2F2) were the resulting gaseous products in the vacuum pyrolysis of cathode materials. At the same time, the gaseous product species and relative yield were significantly affected by pyrolysis temperature. Combined with the GC-MS analysis of pyrolysis tar obtained from vacuum pyrolysis simulation experiments, it could be inferred that pyrolysis tar was formed as a result of the cleavage and recombination of chemical bonds in solvents. The simulation experiments also showed that the increase of vacuum pyrolysis temperature and decrease of residual gas pressure enhanced the recovery efficiency of cathode materials. Further, the carbon and fluorine content of the cathode materials were found to decrease slowly during vacuum pyrolysis, while the aluminum content increased. When the vacuum pyrolysis temperature was above 600 °C, Al foils ablated and even melted to strips. The phase composition of cathode materials was still LiFePO4 after vacuum pyrolysis. The leaching performance tests of cathode materials demonstrated that the increase of vacuum pyrolysis temperature and decrease of residual gas pressure can lead to the decrease of leaching efficiency for Fe. This technology offers an efficient way to recycle organic compounds and valuable materials from spent LiFePO4 batteries, and it has been demonstrated to be of good economic benefit and energy savings.