Sulfur nanoparticles/Ti3C2Tx MXene with an optimum sulfur content as a cathode for highly stable lithium–sulfur batteries

Abstract

Lithium–sulfur batteries have a high theoretical energy density but they need better sulfur host materials to retain the lithium polysulfide shuttle effect, which results in the batteries' capacity fading. Titanium carbide MXene (Ti₃C₂T_x MXene) is an excellent host for the sulfur cathode because of its layered-stacked structure and many surface termination groups. The sulfur content in S/Ti₃C₂T_x MXene composites is an important factor affecting the cathodes' electrochemical performance. In this work, S/Ti₃C₂T_x MXene composites with different sulfur contents are prepared by a one-step hydrothermal process, and the influence of the sulfur content in the S/Ti₃C₂T_x MXene composite on the S/Ti₃C₂T_x MXene cathode's electrochemical performance is studied. When the mass ratio of sulfur to MXene in the reactant is 4 : 1, the sulfur nanoparticles are uniformly filled in the layered-stacked structure. The layered-stacked structure can buffer the volume expansion of sulfur during cycling and the surface termination groups exhibit strong adsorption of LiPS_n. Thus, the S/MXene composite with an optimum sulfur content (67.0 wt%) demonstrates an excellent electrochemical performance, including a high initial reversible capacity (1277 mA h g⁻¹ at 0.5 C) and the best cycling performance (1059 mA h g⁻¹ at 0.5 C after 100 cycles). This work offers a guide to developing advanced S-based cathode materials with an appropriate S content for lithium sulfur batteries.