Pyrolysis mechanism of spent LIBs separator and catalytic effect of metal foils: Insights from combined experimental and DFT studies

The rapid development of new energy technologies has facilitated the widespread adoption of electric vehicles, but has also led to a significant increase in the generation of spent lithium-ion batteries (LIBs). Extensive research has been conducted on the recycling of spent LIBs with most studies focusing on the recovery of the anode and cathode materials, electrolytes, and current collectors. Research on the recycling of battery separators remains limited. Pyrolysis technology has been shown to enable the efficient recovery of organic components and has already been applied in the recycling of spent LIB separators. However, existing studies reveal that the mechanisms underlying separator pyrolysis are not well understood, and the role of endogenous metals (Cu and Al foil) in the pyrolysis process remains unclear. Density Functional Theory (DFT) calculations have been extensively employed in mechanistic investigations of organic compound pyrolysis and metal-catalyzed reactions. In this context, the commonly used polypropylene (PP) separator was selected as the subject of this study. Various thermal analysis devices and kinetic methods were employed to investigate the pyrolysis characteristics, pyrolysis kinetics, distribution of pyrolysis products, and the influence of metal foils on the pyrolysis process of PP separators. Through DFT calculations and wave function analysis, the pyrolysis mechanism of PP separators and the catalytic role of metal foils in the PP pyrolysis process were elucidated.