S-doped MXene@porous carbon nano-fiber composite for improved sodium storage performance

Abstract

Sodium-ion batteries have attracted considerable interest of many scholars due to their low cost and similar energy storage mechanism to lithium-ion batteries. Considering the poor electrochemical redox reaction kinetics and low structural stability resulting from the larger radius of Na+ (0.102 nm), we have elaborately designed novel sulfur-doped MXene/porous carbon nano-fiber composites (S-MX@CNF) as anodes for SIBs via a synergistic assembly and sulfidation treatment approach. The S-MX@CNF composites have a multi-layered structure, which not only prevents restacking of MXene layers and increases accessible active sites, but also enhances the overall electrode conductivity. The composites exhibit a unique interconnected conductive network frame structure and increased interlayer spacing, which facilitates fast ionic and electronic transport rates. Additionally, the robust composites exhibit high chemical stability, enabling it to tolerate volume changes during the rapid charge/discharge process. As a result of these synergistic effects, the S-MX@CNF displays a high reversible capacity of 304 mAh/g (0.5 A/g) after 1000 cycles and long cycle stability of 170 mAh/g (3 A/g) with only 0.1 % degradation per cycle within 4900 cycles. This work opens up new opportunities for further advances in synergistic assembly and heteroatom doping strategies for composites in energy storage devices.