S-doped carbon@TiO2 to store Li+/Na+ with high capacity and long life-time

Sodium-ion batteries as the possible replacements of lithium-ion batteries have drawn much attention recently. Although graphite have been the anodes of commercial lithium-ion batteries, it is difficult to reversibly intercalate Na+ of large diameter in graphite with high capacity. In this study, S-doped carbon@TiO2 core-shell composites are designed and prepared via a facile hydrothermal route. The composites as anodes showed high reversible capacities of 768 and 480 mAh g-1 (higher than the theoretical values of both graphite and TiO2) for Li+ and Na+ storage which can be ascribed to the surface storage due to the presence of sulfure atoms. It is discovered that the S-doping can greatly increase the binding energy of Na ion on graphite, and improve the possible formation of C4Na on the surface. In addition, TiO2 nanocoatings have a great effect on the storage stability of both Li+ and Na+ in the composites, resulting in the ultralong cycling life. The synergistic combination of S-doped carbon and TiO2 dense nanocoatings may provide new strategies for the investigation of supercapacitors and other related devices.