Pore-size tuning of hard carbon to optimize its wettability for efficient Na+ storage.

Hard carbons hold great promise as the anode materials for sodium-ion batteries (SIBs), but the limited capacities and sluggish Na⁺ transfer kinetics still hinder their practical applications. These issues can be addressed from the perspective of improving the wettability of hard carbons with electrolyte. Herein, we demonstrate that the wettability of hard carbons can be regulated by tuning their pore size, so as to optimize their electrochemical properties. A series of N-doped hollow mesoporous carbon nanotubes (HMCNTs) with the average pore sizes in the range of 2–8 nm are synthesized. Among them, the HMCNTs with an average pore size of 6.1 nm (HMCNTs-6.1) exhibits the most improved wettability and reaction kinetics, which delivers a high reversible capacity (415.5 mA h g⁻¹ after 100 cycles at 0.1 A g⁻¹), superior long-term cycle stability and rate capability. In addition, as visualized by in situ transmission electron microscopy, the HMCNTs-6.1 with relatively large mesopores is more favorable for the mass transport across the carbon shells than the HMCNTs with smaller pore sizes. This work provides new insight for understanding the relationship between pore size, electrolyte wettability and electrochemical performance of porous hard carbon, which can help to design the high-performance SIB anodes. [ABSTRACT FROM AUTHOR]