Regulating Closed Pore Formation of Cellulose-Derived Hard Carbon toward Better Sodium Storage

Cellulose-derived hard carbon is considered to be one of the most promising anode materials for sodium-ion batteries. However, the formation mechanism of the closed pores, which plays a predominant role in improving sodium storage, remains elusive. In this study, the correlation between the microstructure of the resultant hard carbons and the cellulose precursor is developed. The hydrogen bond network structure of cellulose is transformed by ball milling. Specifically, sufficient active hydroxyl groups are exposed, despite the crystalline components being decreased, contributing to the formation of well-structured carbon layers and abundant closed pores. Meanwhile, the recombination of hydroxyl groups caused by excessive ball milling leads to a reduction in their content and a decrease in the number of closed pores. The optimal sample of hard carbon exhibits the most abundant closed pore structure as well as the highest reversible capacity of 305 mAh g–1 at 30 mA g–1 and an initial Coulombic efficiency of 89%.