Self-supported hard carbon anode from fungus-treated basswood towards sodium-ion batteries

Hard carbon derived from biomass is regarded as a promising anode material for sodium-ion batteries (SIBs) because of its low operating potential, high capacity, resource availability, and low cost. However, scientific and technological challenges still exist to prepare hard carbon with a high initial Coulombic efficiency (ICE), an excellent rate capability, and good cycling stability. In this work, we report a self-supported hard carbon electrode from fungus-pretreated basswood with an improved graphitization degree and a low tortuosity. Compared with the hard carbon derived from basswood, the hard carbon electrode from fungus-pretreated basswood has an improved rate capability of 242.3 mAh·g⁻¹ at 200 mA·g⁻¹and cycling stability with 93.9% of its capacity retention after 200 cycles at 40 mA·g⁻¹, as well as the increased ICE from 84.3% to 88.2%. Additionally, ex-situ X-ray diffraction indicates that Na⁺ adsorption caused the sloping capacity, whereas Na⁺ intercalation between interlayer spacing corresponded to the low potential plateau capacity. This work provides a new perspective for the preparation of high-performance hard carbon and gains the in-depth understanding of Na storage mechanism.