Hybrid energy storage mechanisms for sulfur-decorated Ti3C2 MXene anode material for high-rate and long-life sodium-ion batteries

Sulfur-decorated Ti3C2 MXenes are synthesized via solution soaking method with electrostatic attraction, whereby more sodium-storage situations derived from sulfur groups and more rapid sodium diffusion paths have appeared in sodium-pillared and sulfur-decorated two-dimensional MXenes interlayers. As an anode material for sodium ion battery, sulfur-decorated Ti3C2 MXene renders an impressive reversible capacity of 135 mAh g−1 at a high current density of 2 A g−1 after 1000 cycles, with a low average capacity loss of 0.033% per cycle, and a superior rate capability of 136.6 mAh g−1 at 5 A g−1. The excellent electrochemical performance can be ascribed to distinctive two-dimensional sulfur-decorated Ti3C2 MXenes, self-enhanced kinetic and hybrid energy storage mechanisms, i.e., intercalation pseudocapacitance and surface-controlled pseudocapacitance. These attributes enable sulfur-decorated Ti3C2 MXene to be a promising long-term and high-rate anode material for sodium-ion battery.