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

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, Zn²⁺ 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.