Improved sodium-ion storage performance of Ti₃C₂T_X MXenes by sulfur doping

The sodium storage performance of recently reported Ti₃C₂T_x MXenes is seriously restricted by their low specific capacity due to their insufficient interlayer spacing. Herein, for the first time, a sulfur (S) doped multilayered Ti₃C₂T_x MXene was prepared by a simple sulfidation treatment of Ti₃C₂T_x using thiourea as the S source, which shows an increased interlayer spacing and enhanced electrical conductivity. When used as an anode for sodium-ion batteries (SIBs), the S-doped Ti₃C₂T_x exhibits a high reversible capacity of 183.2 mA h g^-1 after 100 cycles at 0.1 A g^-1, excellent rate capability (121.3 mA h g^-1 at 2 A g^-1 and 113.9 mA h g^-1 at 4 A g^-1) and robust long-term cycling stability with a reversible capacity of 138.2 mA h g^-1 after 2000 cycles at 0.5 A g^-1. Notably, the superior sodium storage performance should be attributed to the multilayered morphology, expanded interlayer spacing and enhanced electrical conductivity as well as the high contribution of surface-induced capacitive behavior after S doping, and it outperforms those of reported Ti₃C₂T_x based electrodes, highlighting the feasibility of the S doping strategy. Most importantly, this work offers a novel approach for smart design and rational fabrication of heteroatom-doped MXenes for energy storage and conversion applications.