Comparative Upcycling of Three Common Plastic Types into Hierarchical Porous Carbon for Zinc–Iodine Batteries

Waste plastics persist in the environment and threaten ecosystems, yet their high carbon content offers an opportunity for value-added upcycling. Here, three representative waste plastics, high-density polyethylene (HDPE), poly(vinyl chloride) (PVC), and poly(ethylene terephthalate) (PET)–are upcycled into hierarchical porous carbons via one-step carbonization-activation, and their performances as cathodes for aqueous zinc–iodine (Zn–I2) batteries are benchmarked. Results indicate that PET-derived porous carbon (PET–PC) exhibits the highest specific surface area, abundant hierarchical pore structure, and excellent graphitization due to its rigid benzene ring structure and ester group self-activation. This significantly enhances iodine immobilization capacity and ion transport kinetics. Electrochemical testing revealed that the PET–PC cathode maintained a specific capacity of 125.5 mAh g–1 and a capacity retention rate of 88.1% after 2000 cycles at a current density of 5 A g–1, demonstrating outstanding cycling stability and rate performance. This study provides a strategy for the high-value utilization of waste plastics and offers theoretical foundations and practical references for cathode material design in zinc–iodine batteries.