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.

In this investigation, a novel process for the synthesis of nano-ZrO₂ powders based on high-temperature mechanochemical technology (HTMT) in a short process is proposed and HTMT nano-ZrO₂ enhancement mechanism as an additive on the properties of B₄C ceramics was systematically investigated. ZrO(OH)₂ was used as a precursor, and ZrO₂-B₄C composites were prepared by optimizing the ball milling temperature and time in combination with the hot-press sintering technique. The results demonstrated that the high-temperature mechanical force causes the transition temperature of ZrO₂ from monoclinic to tetragonal crystal system to be decreased to 500 °C. The ZrO₂ treated by high-temperature ball milling at 600 °C/6 h exhibits lower microstress, higher crystallinity, and a particle size of only about 9.12 nm. HTMT nano-ZrO₂ effectively controls the size of in situ generated ZrB₂ particles in B₄C ceramics, reduces interfacial porosity and grain coarsening, and promotes densification of B₄C ceramics compared to commercially available nano-ZrO₂. With the addition of 4 wt% HTMT nano-ZrO₂, the composite showed optimal comprehensive properties: relative density of 99.75% (2.57 g/cm³), fracture toughness of 4.74 MPa/m^1/2, flexural strength of 266.61 MPa, Vickers hardness of 31.14 GPa, and fracture mode with mixed mechanism of through-crystallization and along-crystallization.