A Dual‐Phase Pore Engineering Strategy to Enhance Low‐Voltage Plateau Capacity of Hard Carbon for Sodium‐Ion Batteries

ABSTRACT Hard carbon is the most commercially viable anode material for sodium‐ion batteries (SIBs), and yet, its practical implementation remains constrained by insufficient low‐voltage plateau capacity, a critical parameter governing storage capacity. This study introduces a targeted component removal and chemical etching strategy to precisely tailor the porous structure of hard carbon and thus remarkably enhance the plateau capacity. In this strategy, alkaline‐dissolved components are removed to form a closed‐pore core with tunable size. Subsequently, the in situ occupied alkaline engineers the pore structure through chemical etching. The optimized hard carbon material not only has short‐range disordered graphite domains to facilitate Na ⁺ ions' intercalation and deintercalation but also has abundant micropores and closed‐pore structures with appropriate pore sizes and an ultrathin carbon layer (1−3 layers) to significantly increase the sodium storage sites. The resulting hard carbon delivers a high reversible specific capacity of 389.6 mAh g ⁻¹ with a low‐voltage plateau capacity as high as up to 261.5 mAh g ⁻¹ and an initial Coulombic efficiency of 90.7%. Crucially, this cost‐effective methodology shows broad precursor adaptability across lignocellulosic biomass, establishing a universal paradigm for designing high‐performance carbonaceous anodes for SIBs.