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

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.