Closed-Pore Hard Carbon Nanospheres via Aldol Condensation for Sodium Storage

The closed pores resulting from distortion of the graphite domain structure are crucial for enhancing the reversible capacity of sodium storage in the hard carbon plateau region, as well as achieving a high initial Coulombic efficiency. In this study, we propose a method to enhance the reversible capacity of sodium storage in the hard carbon nanosphere plateau region by utilizing terephthalaldehyde (C8H6O2) and resorcinol (C6H6O2) for modulating closed pore size and graphite domain distribution through an aldol condensation reaction. The structural characterization reveals that an increase in the proportion of sp2 C in the precursor structure leads to graphite domains that are more easily twisted, leading to the formation of closed pores with smaller sizes during high-temperature pyrolysis. The target sample (PRHC-1500) exhibits a plateau capacity proportion of 59.23% and an initial Coulombic efficiency (ICE) of 81.14% in the half-cell. Additionally, the Coulombic efficiency remained at 100% even after undergoing 1000 cycles at a current density of 1600 mA g–1, thereby demonstrating exceptional cycling performance. This paper presents a valuable reference for modulating the closed-pore structure in hard carbon nanospheres by carefully selecting appropriate precursors.