A Stage‐Wise Plateau‐Sodiation Mechanism Enabled by Ultramicropores in the Hard Carbon Anode for Sodium Storage

ABSTRACT Hard carbon is a promising anode for emerging sodium‐ion batteries, yet the sodium storage mechanism, particularly in the low‐potential plateau region, remains debatable. Herein, hard carbon with rich pores, primarily ultramicropores (<0.7 nm), is synthesized via a self‐sacrificed template strategy. Through combined electrochemical analysis and in situ characterizations, a direct correlation between pore architecture and plateau‐region sodium storage is established. Crucially, a two‐stage “intercalation/filling–filling” sodiation mechanism in the plateau region is disclosed, which divides the plateau sodiation process into distinct phases for the first time. This stage‐wise mechanism enables pores to be fully involved throughout the plateau, resulting in the hard carbon with a high reversible capacity of 402.3 mAh g ⁻¹ and exceptional rate capability. This work enriches fundamental insights into the sodium storage mechanism of hard carbon, providing a blueprint for the versatile design of advanced anode materials.