Thermal decomposition of spent lithium-ion batteries pouch: Investigating kinetic and thermodynamic compensation effects

A deeper understanding of the pyrolysis process for main and additional components in spent lithium-ion batteries (LIBs) could provide valuable insights for optimizing their recycling processes. This study examined the thermal behavior, kinetics, thermodynamics, and product evolution during the pyrolysis of laminate pouch primarily composed of polypropylene and polyamide. The kinetic compensation effect (KCE) and thermodynamic compensation effect (TCE) were also probed to provide a comprehensive understanding of the conversion. The degradation process was divided into three stages, with total mass loss ranging from 31.14 to 40.28 % and peak temperatures between 419 and 472 °C. The average activation energy was determined to be 118.06 kJ mol⁻¹, with specific values of 99.25, 119.06 and 139.31 kJ mol⁻¹ within conversion rate of 0.10–0.30, 0.35–0.75 and 0.80–0.95, respectively. The pouch conversion followed D1 diffusion mechanism. The KCE was confirmed and reconstructed f(α) = α^0.45316 (2α^1.55)^-1 displayed an excellent fit. Thermodynamic analysis implied that this conversion process was endothermic and non-spontaneous. Enthalpy and entropy relationship demonstrated the existence of T_EC with compensation temperature (T_comp) and experimental temperature (T_exp) of 676.20 K and 693.23 K, respectively. In addition, free energy of compensation (ΔG_comp) was found to be 164.51 kJ mol⁻¹, in agreement with experimental binding free energy (ΔG_exp) range of 166.48–170.65 kJ mol⁻¹, further confirmed the validity of the adopted mechanism.