Upcycling Fungal Mycelium Into Hard Carbon With Zn‐Engineered Graphitic Nanodomains for Ultrafast Sodium Storage

ABSTRACT Hard carbon anodes are promising candidates for sodium‐ion batteries but still suffer from limited capacity and rate capability. Here, we propose fungal mycelium, an abundant and low‐cost biomass precursor, for the fabrication of high‐performance hard carbon. Through alkali treatment, Zn 2+ biosorption and carbonization at 1300°C, we obtain zinc‐modified hard carbon (Alkali‐FC‐Zn). This process embeds Zn during carbonization and generates short‐range‐ordered graphitic nanodomains within an amorphous matrix, with enlarged interlayer spacing and closed micropores. Zinc incorporation increases the graphitization degree and introduces Zn─N, C═O, N─5, and C─P─O surface motifs together with O/N/P heteroatoms, enriching Na + adsorption sites and lowering diffusion barriers. Furthermore, the heteroatom/Zn coordination increases the sloping capacity, and the closes pores provide filling sites for deep Na storage, featuring a cooperative adsorption‐intercalation‐filling mechanism. Collectively, these structural merits promote rapid Na + transport and balanced charge storage. Consequently, Alkali‐FC‐Zn delivers 410 mAh g −1 at 0.05 A g −1 and 90 mAh g −1 at 20 A g −1 at 25°C; at −20°C it provides 312.77 mAh g −1 at 0.03 A g −1 , underscoring temperature‐robust kinetics. This work positions waste fungal mycelium as an eco‐friendly, low‐cost precursor to improve hard‐carbon anode performance and advance sustainable energy storage.