Enhancement mechanism of functionally sulfur-doped TiCT-confined antimony anode in high-performance sodium-ion batteries.

Antimony (Sb), which has a suitable working potential and high theoretical specific capacity, is considered an appropriate anode material for sodium-ion batteries. However, the large volume expansion of Sb causes electrode collapse and capacity decay. In this study, a functionally sulfur-doped TiCT confined Sb composite (Sb/S-TiCT) was designed and prepared. The sulfur-functionalized TiCT improved the charge distribution at the heterogeneous interface while forming more robust chemical bonds (Ti-S-Sb), which inhibited the volume expansion of antimony, increased the sodium storage capacity, improved the charge transfer kinetics, and promoted the intensive adsorption of Na ions at the electrode interface in the electrolyte. Moreover, metal Sb acts as a sodium reservoir, reducing the "sticky" re-stacking tendency of S-TiCT nanosheets and enhancing the electrolyte accessibility. Consequently, the Sb/S-TiCT anode delivered a high reversible capacity (563.5 mAh g at 0.1 A g after 100 cycles) and excellent rate capability (450.9 mAh g at 5.0 A g). The full sodium ion battery of NaV(PO)/C||Sb/S-TiCT achieved high energy density (209.8 Wh kg) and remarkable cycling performance (capacity retention of 81.2 % after 5,000 cycles).