Upcycling of Waste Polymers into Porous Hard Carbon Anodes for Sodium‐Ion Batteries

Hard carbon has recently attracted significant attention as a promising anode material for sodium‐ion batteries (SIBs) due to its high structural stability and appreciable discharge capacity arising from pore filling of Na + . In this work, we synthesized hard carbon by carbonizing waste polymers from waste carbon fiber reinforced plastic. During the carbonization process, the heating rate was carefully controlled to exploit the gas bubbles released from the water retained in the polymers, thereby generating a porous hard carbon. The resulting porous hard carbon was subsequently employed as the anode material for SIBs. Taking advantage of the porous architecture, high‐rate electrochemical testing was performed. Notably, the sample heat‐treated at 1600°C exhibited a reversible capacity of 112.4 mAh g −1 after 700 cycles at 1 A g −1 and maintained as high as 59.1 mAh g −1 even after 7000 cycles at 2 A g −1 , underscoring its remarkable long‐term cycling stability.