Rationally Designing Closed Pore Structure by Carbon Dots to Evoke Sodium Storage Sites of Hard Carbon in Low-Potential Region

Hard carbon (HC) is widely regarded as the most promising anode material for sodium-ion batteries (SIBs). For improving the sodium storage capacity of HC anode, current research primarily focuses on the high-voltage slope region. Actually, increasing the storage capability in the low-voltage plateau region is more important for enhancing the energy density of full cells. Therefore, in this study, HC anode with rich closed pore structure is designed and constructed with the help of carbon dots (CDs), and it is demonstrated that the presence of closed pore structure can provide more sodium storage sites in the plateau region, resulting in an obvious increase of sodium storage capacity. Moreover, the pore-filling and intercalation mechanism for sodium storage in plateau region is revealed by in situ Raman spectroscopy and ex situ transmission electron microscopy (TEM). It is worth noting that the increase in capacity induced by closed pore-filling is not accompanied by a decrease in initial coulombic efficiency (ICE), due to the fact that the introduction of closed pores does not increase the contact area between electrode and electrolyte. This work presents novel concepts for the structural design of HC and provides valuable insights into the effective utilization of plateau region in SIBs. Hard carbon anodes with abundant closed pore structure is designed and constructed by employing carbon dots as pore-forming additives. It is demonstrated that the introduction of closed pore can provide more sodium storage sites in the low potential region through pore-filling mechanism, without the sacrifice of the initial coulombic efficiency.image

Automated summary

The study demonstrates that designing and constructing hard carbon anodes with abundant closed pore structure using carbon dots as pore-forming additives can provide more sodium storage sites in the low potential region, resulting in an increase in energy density of sodium-ion batteries. The research also reveals the pore-filling and intercalation mechanism for sodium storage in the plateau region.