Tuning hard carbon pore structure via water vapor activation for enhanced sodium-ion storage

The precise construction of closed pores in carbon anodes is crucial for boosting low-voltage plateau capacity of sodium-ion batteries (SIBs). Traditional closed-pore fabrication methods often face environmental and economic challenges. To address these limitations, this study proposes an innovative synergistic strategy combining water vapor activation with high-temperature repair. By precisely controlling the steam dosage during the 800 °C pre-carbonization stage, a tunable open pore network was constructed in the material, followed by efficient transformation of these open pores into ultra-micropores and closed pores through 1350 °C high-temperature treatment. The study reveals that the volume and size of open pores during pre-carbonization directly determines the final pore structure characteristics. Excessively large and abundant open pores hinder the transformation of the pore architecture during high-temperature treatment. The optimized PRHC2 anode demonstrates outstanding electrochemical performance, delivering a reversible capacity of 377.6 mAh g -1 at 30 mA g -1 , including 284.1 mAh g -1 contribution from the plateau region. This research not only addresses the constraints of conventional methods but also provides critical technical support for developing next-generation carbon anode materials. This study developed a green, low-cost steam activation-high-temperature repair method to precisely control pore structure, yielding tunable closed-pore hard carbons with 284.1 mAh g -1 plateau and 377.6 mAh g -1 reversible capacity at 30 mA g -1 . • A novel and environmentally friendly water vapor activation-high temperature carbonization repair technique to achieve precise control of hard carbon pore structures was proposed • A new insight into the transformation from open pores to closed pores was provided • PRHC2 with abundant closed pores delivers a remarkable reversible capacity of 377.6 mAh g -1 (with 284.1 mAh g -1 plateau capacity) at 30 mA g -1