Nanoporous carbon nitrides (C6N7, C3N5, C2N) for suppression of the shuttle effect and enhanced performance of Na-Se batteries

Sodium-Selenium batteries (NaSeBs) have recently attracted great research interest as they possess high-energy density and potential sustainability, especially due to abundance of both sodium (Na) and selenium (Se) resources. However, the discharging process produces redox intermediates, sodium poly-selenides (Na2Sen; n = 1-8), which dissolve in the electrolyte and deteriorate the performance and lifespan of NaSeBs. To address this issue, we propose three nanoporous carbon nitride monolayers (C6N7, C3N5, C2N) as cathode additives to suppress the shuttle effect. By using density-functional theory calculations, we investigate the binding energy, band structures, charge exchange and activation barrier energy of dissociation of Na2Sen moiety. Our results show that the interactions of Na2Sen with C6N7, C3N5, and C2N are stronger than their interactions with the commonly used electrolytes. The adsorptions of the Na2Sen cause the metallization of the anchoring materials and the activation energy is found to be reduced, which further improves their conductivities. Among the studied systems, C2N turns out to be the best candidate for a suggestive cathode additive to suppress the shuttle effect and to catalyse the electrochemical process, consequently, enhancing the battery's lifespan.