Thermal Decomposition of Organic Components in Spent Lithium-Ion Batteries: Stagewise Evaluation and Kinetic Analysis

Recycling spent lithium-ion batteries (LIBs) is essential for environmental protection and resource conservation. However, effective removal of organic components such as electrolytes and poly(vinylidene fluoride) (PVDF) from cathode materials remains a challenge, which limits recycling of spent LIBs. This systematically investigates the thermal decomposition behaviors of organic components in spent LIBs under a controlled atmosphere and thermal conditions. Four distinct stages of thermal decomposition were identified, among which proper adjustment of stage IV is crucial for complete decomposition of PVDF. Oxygen presence significantly enhances PVDF decomposition via exothermic oxidation. Specifically, the activation energy required for PVDF decomposition under air conditions ranged from 20.1 to 29.6 kJ/mol, substantially lower than the 180.2 to 197.9 kJ/mol observed under Ar, corresponding to an approximately 85% reduction in activation energy. Oxidative pyrolysis decreased fluorine retention in stable fluorinated intermediates, potentially accounting for approximately 50% lower residual fluorine compared to inert conditions. Consequently, oxidative pyrolysis facilitates the transformation of fluorinated intermediates into stable inorganic compounds such as CO₂ and CF₄, thereby mitigating the environmental risks posed by PFAS precursor retention. These findings support the use of oxygen-rich pyrolysis to enhance organic removal, reduce the PFAS risk, and improve recycling efficiency.