1 Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, 34132, Republic of Korea.
2 Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, QC, H3G 1M8, Canada.
3 Department of Civil & Energy System Engineering, Kyonggi University, Suwon, 16227, Republic of Korea.
4 Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, 34132, Republic of Korea. Electronic address: hjyu@kigam.re.kr.

This study investigates the thermochemical and co-thermochemical conversion of black mass (BM), derived from spent lithium-ion batteries, with and without polyethylene (PE) under various atmospheric conditions (N₂, 25 % CO₂, and 99.999 % CO₂) at temperatures ranging from 700 °C to 900 °C. In an inert N₂ environment, gas emissions were minimal, while significant CO production was observed under CO₂-rich conditions due to the Boudouard and catalytic reactions facilitated by Ni-based components in BM. The addition of PE enhanced the generation of H₂ and CO, particularly under CO₂ environments, through catalytic conversion of pyrolyzed volatiles. Even with low CO₂ concentrations (~18 mol%), considerable CO₂-to-CO conversion was achieved. Heating rate and feedstock ratio (BM:PE) notably influenced gas profiles and syngas yield. Reusability tests showed that processed BM retained partial catalytic activity and maintained structural integrity, making it viable for subsequent hydrometallurgical applications. These results suggest the potential of BM as both a catalyst and a valuable resource for CO₂-assisted syngas production.