Co-upcycling spent lithium-ion batteries and plastics into microwave absorbing materials with Ni-Co catalyst control

Co-upcycling plastics with lithium-ion batteries (LIBs) into carbon nanotubes (CNTs) offers a promising high-value approach; however, it is hindered by the challenge of poisoning metal catalysts by carbon deposition and the uncontrollable particle growth. Here, we propose a co-upcycling strategy to convert spent LiNi_xCo_yMn_1-x-yO₂ (NCM) and binary plastics-polyethylene terephthalate (PET) and other plastics-into NiCoMnO_x/CNTs composites (or materials) for microwave absorption. During the pyrolysis, the generated pyrolysis gas reduces the NCM to NiCoMnO_x and Li₂CO₃, and the NiCoMnO_x catalyzes the decomposition of pyrolysis gas to generate CNTs. Importantly, Li₂CO₃ suppresses the growth of NiCo particles to below 100 nm and PET as both an etching agent and a carbon source, achieving a carbon conversion rate of 33% while preventing NiCoMnO_x poisoning. After heat treatment at 800 °C, the resulting material exhibits favorable microwave absorption with an effective absorption bandwidth (EAB, RL <-10 dB) of 7.01 GHz at 2.41 mm. Life cycle analysis (LCA) shows that this strategy has obvious environmental benefits. Overall, PET is a general enabler to prepare (Ni_xCo_y)MnO/CNTs microwave-absorbing materials harnessing carbon from binary plastics and critical metals from battery materials, providing a sustainable solution for upcycling spent LIBs and plastic wastes.