Gas evolution characterization and phase transformation during thermal treatment of cathode plates from spent LiFePO4 batteries

Abstract

In this paper, thermal reaction behaviors and gas evolution characteristics of cathode electrodes separated from spent LiFePO4 batteries were systematically characterized using thermogravimetric-differential scanning calorimetry analysis coupled with mass spectrometry equipped with electron ionization system (TG-DSC-EI-MS). TG-DSC-EI-MS analysis indicated tail gases were mainly released in a low-temperature range of 60−250 °C, which attributed to the hydrolysis and decomposition reactions of lithium salt electrolyte. Additionally, H2O, HF and CO2 were detected at the range of 380−600 °C, which responded to thermal decomposition of the binder. H2O and CO2 were the main gaseous products at around 520 °C, which might be released from the oxidation combustion reactions of the binder. At the same time, phase transformation of the cathode active material during thermal treatment was further investigated by SEM-EDS, FT-IR, XRD and Mössbauer spectrum analysis techniques. The results indicated LiFePO4 was oxidized to Li3Fe2(PO4)3 and Fe2O3 during the heating process.