Two-dimensional titanium carbide (Ti₃C₂T) MXenes to inhibit the shuttle effect in sodium sulfur batteries

Room-temperature sodium sulfur batteries (RT-NSBs) are among the promising candidates for large-scale energy storage applications because of the natural abundance of the electrode materials and impressive energy density. However, one of the main technical challenges of RT-NSBs is the shuttle effect by which active redox intermediates (i.e., sodium polysulfides Na₂S, n = 1-8) are dissolved in electrolytes, which hamper the battery reversibility. The interfacial interplays between Na₂S and the electrodes (or electrolytes) at the atomic level thus play an intrinsic role in elucidating the shuttle effect. This work reports the ab initio calculations to unravel the suppression of the shuttle effect using titanium carbide MXenes (Ti₃C₂T, T = F, O) as the cathode additives. The findings reveal that the shuttle phenomenon is efficiently resolved because the immense chemical bonding of Na₂S-Ti₃C₂T interfaces competitively surpasses the binding magnitudes of Na₂S-electrolyte interaction. The analysis of the electronic density of states and charge density further manifests that there is charge donation from the Na-3s orbital of Na₂S to the unfilled F(O)-2p orbitals of metallic Ti₃C₂T. The metallicity of the Ti₃C₂T remains preserved during the entire course of the redox process, ensuring the rapid electrochemical kinetics. Furthermore, the presence of Ti₃C₂T additives drastically reduces the dissociation barrier of the final redox product Na₂S, yielding the efficient utilization of sulfur during the discharge process. This work has proposed the unexplored functionality of Ti₃C₂T as the anchoring materials for RT-NSBs.