S-doped Ti3C2F2 MXene as an ideal sulfur cathode host for high-performance rechargeable lithium–sulfur batteries

Abstract

An ideal host for sulfur cathodes in rechargeable lithium–sulfur batteries (RLSBs) should concurrently possess all the following features: a high electrical conduction, suppression of the shuttle effect, a fast charging/discharging process, a fast ion/polysulfide diffusion, and a substrate for 3D Li₂S deposition. Unfortunately, such a material has not been found. Herein, we first investigate the role of Ti₃C₂T₂ as a host for sulfur cathodes in RLSBs. We reveal that Ti₃C₂F₂ allows a fast Li₂S migration. Ti₃C₂(OH)₂ is reduced by Li₂S towards forming Ti₃C₂O₂. However, Ti₃C₂O₂ and Ti₃C₂S₂ strongly anchor Li₂S, resulting in the rapid passivation of conductive MXene. Therefore, we propose mixed surface terminations by doping O or S into Ti₃C₂F₂. Importantly, S@Ti₃C₂F₂ not only shows a 3D deposition mode, but also significantly accelerate charging/discharging kinetics. Furthermore, the shuttling can also be suppressed effectively. Therefore, S@Ti₃C₂F₂ shows all the features that are required as an ideal sulfur cathode host, thus promising for use in high-performance RLSBs.