Low‑temperature pyrolysis‑derived hard carbon nanosheets with single‑atom Fe‑catalyzed localized graphitization for improved sodium-ion storage

Hard carbon (HC) is a promising anode for sodium‑ion batteries (SIBs), yet achieving high performance via low‑temperature synthesis remains challenging. Here, HC nanosheets with localized graphitization are fabricated through single‑atom‑Fe‑catalyzed pyrolysis at 750 ℃. Atomic‑scale dispersion of Fe in an Fe–O–P coordination environment is confirmed by high-angle annular dark field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and synchrotron X‑ray absorption spectroscopy. The Fe single atoms induce short‑range graphitization, creating extra active sites for reversible sodium-ion storage. Accordingly, the Fe-HC anode delivers 141 mAh g −1 at 5 A g −1 , maintains 209.6 mAh g −1 at 0.5 A g −1 after 400 cycles, and retains high reversibility at − 10 ℃. Detailed electrochemical and structural analyses further elucidate the sodium-ion storage mechanism.