Co-pyrolysis of polypropylene and spent Li-ion battery cathodes: A combined metallurgy approach to recover valuable metals

Abstract

Recycling spent lithium-ion batteries (LiBs) is crucial for the sustainable usage of critical raw materials present in the cathode. The combined metallurgy process is gaining significant attention in achieving this goal. The process includes thermal reduction followed by an environmentally friendly leaching process. In this work, the technological feasibility of a co-pyrolysis method is investigated for the recovery of Li₂CO₃ and transition metals from Li_1-xNi_yMn_zCo_1-y-zO₂ (NMC) based cathode black mass (CBM) obtained from spent LiBs. We analyze the performance of polypropylene as a reducing agent during co-pyrolysis at 500 – 650 °C to reduce NMC. During co-pyrolysis, the reductive gases (H₂ and CH₄) generated from polypropylene reduce NMC at 550 – 650 °C into Ni-Co, MnO, and Li₂CO₃. However, an additional product, NiO and spinel NMC, appeared in co-pyrolyzed CBM at 500 °C. The magnetic fraction of the co-pyrolysis product was separated by water leaching, and then the leach solution was dried to recover Li₂CO₃. The lithium leaching efficiency achieved from the cathode black mass of NMC batteries is 92.80 ± 3.22 wt%. A liquid fuel obtained as a by-product of co-pyrolysis has a gross calorific value of 48 MJ/kg. The process promotes sustainability by efficiently reducing NMC at lower temperatures and producing a liquid by-product for fuel applications.