Microstructural Modulation for Sodium Storage and Rapid Synthesis of Hard Carbon via Electron‐Beam Sintering

ABSTRACT Systematically investigating a strategy for preparing hard carbon and tailoring its microstructure via high‐energy electron‐beam rapid sintering (EBM dynamic annealing) to overcome limitations of conventional tube‐furnace, long‐duration high‐temperature treatments, excessive microcrystal growth and pore collapse. By applying an instantaneous heating‐rapid cooling protocol at 1300°C for only 5 min, we achieve rapid carbonization and microstructural reconstruction of a bamboo‐powder precursor. HRTEM, small‐angle x‐ray scattering (SAXS) and BET analyses reveal an enlarged interlayer spacing (up to 0.372 nm), optimized distributions of open and closed pores, and retention of an appropriate defect concentration; depth‐profiling XPS indicates formation of a thinner, denser solid‐electrolyte interphase (SEI) enriched in inorganic NaF. Electrochemical measurements show that the EBM‐40mA‐5 min hard carbon exhibits a high reversible capacity of 332 mAh·g −1 , the lowest charge‐transfer resistance and the highest Na + diffusion coefficient among all samples; in pouch cells paired with an NNFM cathode, the material retains approximately 81% of its capacity after 1000 cycles at 0.5 C. Mechanistic analysis suggests that the combination of instantaneous high temperature and non‐equilibrium quenching promotes preservation of advantageous micro/mesopores, expansion of interlayer spacing and formation of continuous conductive networks factors that together facilitate the “insertion–pore‐filling” cooperative sodium‐storage mechanism while the optimized SEI reduces interfacial activation energy, thereby substantially improving rate capability and cycling stability.