P-block tin single atom catalyst for improved electrochemistry in a lithium–sulfur battery: a theoretical and experimental study

Abstract

Main group metals are routinely considered as catalytically inactive. Hence, they are never employed for optimizing lithium-sulfur electrochemistry. Herein, density functional theory calculations reveal that atomically dispersed tin on a nitrogen-doped carbon substrate is expected to be highly active for electrocatalysis because of the activation of underfilled p orbitals and a significant shift of the p band center towards the Fermi level upon metal–support interaction. Under theoretical guidance, we prepared a p-block tin single atom catalyst (Sn_SA–NC) with Sn–N₄ as the active site for effectively improving the lithium–sulfur battery performance. The charge transfer between the Sn atom and N ligands creates a highly polar site that exhibits strong adsorption capability towards the electrolyte-soluble long-chain polysulfides. The unique p band structure of the central Sn atom modulates the energy barriers for the rate-determining steps of sulfur redox, thus facilitating the lithium polysulfide conversion. Besides, the exposure and utilization of Sn–N₄ sites are maximized by virtue of the 13 nm thick nanosheet morphology of the carbon substrate. Remarkably, the functional separator modified by Sn_SA–NC increases the sulfur utilization by 79.7%, and endows the lithium-sulfur cells with significantly enhanced cyclability and rate performance. This work successfully expands the employment of main group metals for electrocatalysis applications.