Influence of Particle Size of Lignite‐Based Hard Carbon on Sodium Storage Performance

Abstract The particle size of hard carbon used as an anode material for sodium‐ion batteries (SIBs) directly affects critical physical properties, including specific surface area and conductivity of the electrode, thereby influencing the electrode's sodium storage performance. However, related research is limited. In this work, lignite‐derived hard carbons with various particle sizes were investigated as anode materials for SIBs. The electrochemical performance and Na + diffusion capability were evaluated. The results show that smaller particle sizes in hard carbon anodes lead to reduced mesopore volumes, specific surface areas, and coating densities, which effectively improve cycle stability, initial coulombic efficiency (ICE), and rate capability of the electrode. Specifically, hard carbon anodes within a 1–15 µm particle size distribution exhibited a reversible capacity of 251 mAh g −1 and an ICE of 73.67% at a current density of 25 mA g −1 . Even after 100 cycles at 0.2 C, these anodes maintained a reversible capacity of 238 mAh g −1 , achieving a capacity retention rate of 99.85%.