Suppression of shuttle effect of Na-S batteries using monolayer and bilayer Ti₃C₂F(OH) MXene as an anchoring material

Sodium sulfur batteries that operate at room temperature (RT) have been proposed as a solution to handle large scale energy storage applications. This popularity has been fuelled by the remarkable energy storage density and by the abundance of the electrode materials in the Earth’s crust. However, one of the main challenges faced by RT sodium sulfur batteries is the shuttle effect caused by the six sodium polysulfides (NaPS) Na₂Sn, n = 1–8, which when dissolved in the electrolytes (namely DOL, DME), largely hinder the capacity of the battery. Therefore, the electrode interface plays a crucial role in controlling the shuttle effect. The present work focusses on realistic DFT modelling of suppression of shuttle effect by using 4x4 samples of single and bilayer Ti₃C₂F(OH). The bonding between the NaPS and the monolayer Ti₃C₂F(OH) is stronger than the NaPS-electrolyte interaction. The strength of bonding increases as we move to the bilayer Ti₃C₂F(OH) structure. The strength of the interaction can be attributed to the significant charge transfer from the Na atoms to the functional groups (F/OH) as assessed by Bader charge analysis. The NEB studies demonstrate the lowering of the dissociation barrier of an Na₂S molecule on the surface of Ti₃C₂F(OH) to 0.835 eV from 2.44 eV (for isolated Na₂S) thereby facilitating accelerated electrode kinetics and higher utilization of sulfur.