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.

The development of new sodium ion battery (SIB) cathodes with satisfactory performance requires an in-depth understanding of their structure-function relationships, to rationally design better electrode materials. In this work, highly ordered, honeycomb-layered Na₃Ni₂SbO₆ was prepared to elucidate the structural evolution and Na⁺ kinetics during electrochemical desodiation/sodiation processes. Structural analysis involving in situ synchrotron X-ray diffraction (XRD) experiments, electrochemical performance measurements, and electrochemical characterization (galvanostatic intermittent titration technique, GITT) methods were used to obtain new insights into the reaction mechanism controlling the (de)intercalation of sodium into the host Na_3-xNi₂SbO₆ structure. Two phase transitions occur (initial O′3 phase → intermediate P′3 phase → final O1 phase) upon Na⁺ extraction; the partial irreversible O′3-P′3 phase transition is responsible for the insufficient cycling stability. The fast Na⁺ mobility (average 10^–12 cm²·s^–1) in the interlayer, high equilibrium voltage (3.27 V), and low voltage polarization (50 mV) establish the linkage between kinetic advantage and a good rate performance of the cathode. These new findings provide deep insight into the reaction mechanism operating in the honeycomb cathode; the present approach could be also extended to investigate other materials for SIBs.