Ultrahigh Plateau‐Capacity Sodium Storage by Plugging Open Pores

Abstract Hard carbon (HC) stands out as the most promising anode material for sodium‐ion batteries (SIBs), and a precise adjustment of the pore structure is the key to achieving high plateau‐capacity. In this work, composite hard carbon is developed by integrating graphitic carbon with biomass waste (banana peel)‐derived activated carbon (AC). In this design, N‐doped pseudographite layer is stacked at the entrance of open pores, forming a long‐range graphitic layer without excessive graphitization. As a result, the surface area of AC is decreased by 170 times down to less than 10 m 3 g −1 , and the corresponding open pores are in situ converted into closed pores. In an optimized electrolyte solvation structure, the obtained HC anode achieves the reversible sodium‐storage capacity up to 524 mAh g −1 . In particular, a large portion of the capacity (490 mAh g −1 ) lies below the plateau of 0.25 V, which originates from the pore‐filling mechanism as revealed by in situ Raman. This study provides a straightforward method to modulate the pore structure of carbon materials, and an energy‐efficient (900 °C) synthesis for HC compared to traditional high‐temperature routes (e.g., ≈1300–2000 °C).