In this study, we upcycled waste polyethylene (PE) foam into a hard carbon anode material for sodium-ion batteries (SIBs) via sulfonation and subsequent carbonization. Following an optimized sulfonation process (100 °C, 24 h), the sample carbonized at 800℃ (PE_C800) demonstrated the best performance, showing a high reversible capacity of 180 mAh·g− 1 at 0.1 C, excellent rate capability, and long-term cycling stability (93.3% retention after 100 cycles). Structural analysis revealed this sample possessed a hierarchical porous structure and an interlayer spacing (0.388 nm), suitable for Na+ insertion. Through cyclic voltammetry (CV) kinetic analysis and ex-situ Raman spectroscopy, the sodium storage was determined to follow an “adsorption-insertion model”, combining surface adsorption and interlayer insertion. This work presents a practical route for converting plastic waste into high performance energy storage materials.

Sodium-ion batteries (SIBs) have emerged as a promising alternative to lithium-ion batteries due to the natural abundance and low cost of sodium resources. However, the relatively large ionic radius of sodium ions hinders their intercalation into conventional graphite anodes, necessitating the development of advanced anode materials. In this study, high-performance hard carbon materials were synthesized from ZIF-8 precursors through controlled carbonization at various temperatures. Among the samples, ZIF-800, which is carbonized at 800 °C, exhibited the highest reversible capacity (156.63 mAh/g after 100 cycles at 100 mA/g) and excellent cycling stability. This superior performance is attributed to the optimized combination of high specific surface area (700.35 m2/ g), well-developed pore structure, and enhanced defect concentration, as indicated by a low IG/ ID ratio. The capacitive-dominant charge storage behavior further contributes to the improved electrochemical characteristics. These findings highlight the critical role of tuning carbonization temperature to achieve a balanced microstructure, offering valuable insights for the rational design of high-performance hard carbon anodes for SIBs.