Engineering Pore Architecture in Hard Carbon for High‐Performance Sodium‐Ion Batteries: Distinguishing the Contributions of Ultramicropores and Closed Pores

Abstract Hard carbon (HC) stands as a leading anode candidate for sodium‐ion batteries, yet the specific functions of its multiscale pore structure, especially ultramicropores (< 0.7 nm), have remained contentious. Herein, the distinct functions of different pores (open pores, sub‐0.7 nm ultramicropores, and closed pores) are elucidated through the rational design of model HC materials derived from a homologous zinc gluconate. It is demonstrated that closed pores (2–3 nm) serve as the dominant contributor to the low‐voltage plateau capacity via quasi‐metallic sodium cluster formation. Ultramicropores significantly enhance the initial Coulombic efficiency (ICE, up to 93.5%) by enabling selective desolvated Na ⁺ access while restricting electrolyte ingress, though they contribute only secondarily to the plateau capacity via adsorption. In contrast, open pores exacerbate irreversible electrolyte decomposition, impairing ICE. The optimized material, ZHC600‐1300, delivers a high reversible capacity of 414.8 mAh g ⁻¹ , an exceptional ICE of 93.1%, a superior plateau capacity (306 mAh g ⁻¹ ), and remarkable cycling stability. When configured in full cells, it delivers a high energy density of 321.5 Wh kg ⁻¹ , demonstrating great potential for practical applications. This work provides fundamental insights into pore‐dependent sodium storage mechanisms and establishes a design principle for high‐performance HC anodes.