Superior anchoring of sodium polysulfides to the polar C₂N 2D material: A potential electrode enhancer in sodium-sulfur batteries

Despite the high theoretical specific energy in rechargeable sodium-sulfur batteries, the shuttle effect severely hampers its capacity and reversibility, which could be overcome by introducing an anchoring material. We, herein, use first-principles calculations to study the low-cost, easily synthesized, environmentally friendly, and stable two-dimensional polar nitrogenated holey graphene (C2N) and nonpolar polyaniline (C3N) to investigate their performance as anchoring materials and the mechanism behind the binding to identify the best candidate to improve the performance of sodium-sulfur batteries. We gain insight into the interaction, including the lowest-energy configurations, binding energies, binding nature, charge transfer, and electronic properties. Sodium primarily contributes to binding with the nanosheets, which is in accordance with their characteristics as anchoring materials. Sodium polysulfides (NaPSs) and the S8 cluster adsorb at the pores of C2N, where there are six electron lone pairs, one for each N atom. The polar C2N binds the NaPSs much strongly than the nonpolar C3N. In contrast to C3N, the charge population substantially modifies by adsorbing NaPSs on C2N, with a substantial charge transfer from the sulfur atoms. The calculated work function of 6.04 eV for pristine C2N, comparable with the previously reported values, decreases on adsorption of the NaPSs formed from battery discharging. We suggest that the inclusion of C2N into sulfur electrodes could also improve their issue with poor conductivity.