Closed Pore Architecture and Sodium Cluster Deposit Visualization in Hard Carbon

Achieving the full potential of hard carbon (HC) for sodium storage requires a deep understanding of its complex porous structure as well as charge storage mechanism. While the contribution of sodium deposition within HC pores to the overall capacity is recognized, detailed visualization and mechanistic understanding of this process remain challenging. This study leverages advanced electron microscopy techniques to probe the intricate pore architecture of HC and directly visualize sodium storage within its pores. By employing an HC material (PHC-1) with rich closed pores as the platform material, electron tomography is utilized to reconstruct the pore architecture of PHC-1, providing quantitative insights into porosity, pore size, and pore structure. Low-dose electron microscopy visualizes metastable sodium clusters filling up within the pores during sodiation. Complementary in-situ and ex-situ characterizations further elucidate the synergistic adsorption-intercalation-filling mechanism of PHC-1. This contribution provides significant insights into the structure-property correlation of HC.