Liquid-phase carbonization strategy to recycle waste PET into defect-rich hard carbon for ultralong cycle life sodium-ion battery

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Hard carbon (HC) is widely regarded as one of the most promising anode materials for commercial sodium-ion batteries due to its excellent electrochemical performance and cost-effectiveness. Although organic polymers offer compositional homogeneity and structural tunability as HC precursors, their high raw material costs and uncontrollable carbonization processes limit large-scale applications. Here, we introduce a liquid-phase carbonization strategy to recycle waste polyethylene terephthalate (PET) into porous micro/nanostructured HC enriched with intrinsic carbon defects (LHC-3, LHC = liquid-phase-prepared hard carbon). These carbon defects and the morphological structures were modulated by bubbles generated from the decomposition of PET in the presence of N,N’-dimethylformamide and zinc acetate. The synergistic effects between intrinsic carbon defects and micro/nanostructure endow LHC-3 anode with high specific capacity (355 mAh·g⁻¹ at 0.1 A·g⁻¹), superfast charging capability (132.6 mAh·g⁻¹ input within 13 s of charging), and ultralong cycling stability (100,000 stable cycles at 50 A·g⁻¹). The sodium storage mechanism of LHC-3 anode was investigated by ex-situ Raman spectroscopy, X-ray photoelectron spectroscopy, and ion diffusion kinetics analysis. Theoretical calculations indicate that intrinsic carbon defects with non-zero curvature structure in LHC-3 enhance its ability to accommodate more Na⁺. These findings are expected to have broader applications in energy storage and waste management.