Recycling polyvinyl chloride plastics into hard carbon: influence of functional groups on structural and electrochemical properties

• • Triple-functionalization (dichlorination, sulfonation, N-doping) of PVC yields hard carbon with 25% carbon yield, avoiding toxic dioxin emissions, addressing both waste management and resource recovery. • • The engineered hard carbon exhibits a reversible capacity of 355 mAh g−1 at 0.1 A g−1, equivalent to 95.4% of graphite's Li-ion capacity, demonstrating commercial viability for sodium-ion anodes. • • Long-term cycling stability: 216 mAh g−1 retained after 1000 cycles at 1.0 A g−1 (70.1% capacity retention), indicating robust structural integrity for grid-scale storage. • • High-rate capability: 188 mAh g−1 at 5.0 A g−1, enabled by closed pores (~2.55 nm) and expanded interlayer spacing (0.382 nm), facilitating rapid Na+ transport.