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.

Transforming polyethylene foam into a hard carbon anode: a study on its structure and sodium storage behavior
    Abstract
    1 Introduction
    2 Results and discussion
        2.1 Physical properties of PE foam and hard carbons
        2.2 Electrochemical performances of hard carbons
        2.3 Analysis of Na+ storage mechanism
    3 Conclusion
    4 Experimental section
        4.1 Synthesis of PE foam-derived hard carbons
        4.2 Material characterization
        4.3 Electrochemical measurements
    References

• Kitak Kim(Department of Materials Science and Engineering, Myongji University, Yongin-si 17058, Gyeonggi-do, Republic of Korea)
• Seunghoon Nam(Department of Materials Science and Engineering, Myongji University, Yongin-si 17058, Gyeonggi-do, Republic of Korea) Corresponding author
• Seungjae Moon(Department of Chemical Engineering, Myongji University, Yongin-si 17058, Gyeonggi-do, Republic of Korea)
• Suah Park(Department of Chemical Engineering, Myongji University, Yongin-si 17058, Gyeonggi-do, Republic of Korea)
• Yongjun Yang(Department of Chemical Engineering, Myongji University, Yongin-si 17058, Gyeonggi-do, Republic of Korea)
• Seung Gun Kim(Department of Chemical Engineering, Myongji University, Yongin-si 17058, Gyeonggi-do, Republic of Korea)
• Heewon Jin(Department of Chemical Engineering, Myongji University, Yongin-si 17058, Gyeonggi-do, Republic of Korea)
• Sang Eun Kim(Department of Chemical Engineering, Myongji University, Yongin-si 17058, Gyeonggi-do, Republic of Korea)
• Dalsu Choi(Department of Chemical Engineering, Myongji University, Yongin-si 17058, Gyeonggi-do, Republic of Korea) Corresponding author