Elimination of volatile components in cellulose enabling ultrahigh initial Coulombic efficiency in sodium-ion batteries

Hard carbon has emerged as a promising anode material for sodium-ion batteries (SIBs) due to its low working potential and cost-effectiveness. However, its commercialization is hindered by suboptimal initial Coulombic efficiency (ICE) and practical reversible capacity. To address these limitations, we propose a vacuum-modulated pre-carbonization strategy to optimize the adsorption-intercalation sodium storage behavior for hard carbon with ultrahigh ICE. This strategy effectively utilizes volatile components during the pyrolysis process, constructs hierarchical open-pore networks with interconnected channels on the surfaces of the carbon matrix, and then produces hard carbon materials with closed-pore and a moderate degree of graphitization through high-temperature carbonization. Furthermore, the surface oxygen-containing functional groups are also optimized in this process. As a result, the optimized hard carbon anode (CS-2C-0.06P) achieves enhanced ICE in the slope (2.0-0.1 V) and capacity in the plateau (0.1-0.0 V) regions, with the plateau capacity exhibiting nearly fully reversible characteristics. The resulting anode achieves an ICE exceeding 95% with a high reversible capacity of 331.54 mAh g^-1, surpassing those of most previously reported biomass‐derived hard carbons. This work establishes a novel paradigm for designing advanced carbonaceous materials through synergistic optimization of adsorption-intercalation-filling storage behavior, providing critical insights for developing high-energy-density SIBs.