Carbon microspheres with gigapores for application as electrode-active material of sodium-ion batteries

Abstract

Micro- and mesoporous carbons are known to be effective anode materials for sodium-ion (Na+) batteries (SIBs). In contrast, macroporous and gigaporous carbons have rarely been studied for this purpose, even though their porous structure may facilitate electrolyte infiltration to enhance cell performance. Here, a series of gigaporous carbon microspheres (GCS) was synthesized by carbonizing gigaporous polymeric microspheres at different temperatures (700–2500 °C) and adopted as anode-active material of SIBs. All GCS samples exhibited a particle size of 10–15 μm and an average pore size of 0.3–0.5 μm. Nevertheless, their specific surface areas decreased over a large range with increasing carbonization temperature from >400 m2 g−1 to <30 m2 g−1. The GCS samples fabricated at higher temperatures demonstrated better electronic conductivity and a larger contribution from Na + insertion/extraction instead of adsorption/desorption to the capacity of constructed cells during charge/discharge. GCS carbonized at 850–1000 °C resulted in cells with the best capacity performance (>300 mAh g−1). The reason is that GCS produced at lower temperatures had insufficient conductivity and underwent limited electrochemical reactions with Na+, leading to a low capacity. On the other hand, an excessively high carbonization temperature produced carbons having a small d-spacing and lacking the beneficial carbonyl groups, which hindered both Na+ insertion/extraction and adsorption/desorption and therefore also reduced the cell capacity.