Understanding the role of lithium bonds in doped graphene nanoribbons as cathode hosts for Li-S batteries: A first-principles study

Using first-principles calculations, we investigate a family of doped graphene nanoribbons (GNRs) for their suitability as cathode hosts in lithium-sulfur batteries. We probe the role played by the lone pairs of the dopants in confining the lithium polysulfides (LiPS) to understand the mechanism of binding. Our results show that the Li bond between the polysulfides and the doped GNRs is analogous to a hydrogen bond and also dipole-dipole interactions play a key role in anchoring the polysulfides. A critical donor-Li-acceptor angle of 180 degrees is found to be essential for proper adsorption of LiPS, highlighting the importance of the directionality of lone pairs. The charge lost by the sulfur atom of the polysulfide upon adsorption and shape of the lone pair basins and the value of Electron Localization Function (ELF) at the dopant position can provide a quick estimate of the strength of the bond. Significant contractions in the ELF profiles are also observed upon Li2S adsorption, further providing evidence for the hydrogen bond-like nature of the Li bond. Our results corroborate the fact that all acceptors capable of forming hydrogen bonds can be employed as suitable dopants for carbon-based cathode hosts in Li-S batteries.

Automated summary

The study shows that hydrogen bond-like Li bonds and dipole-dipole interactions play key roles in anchoring polysulfides, highlighting the importance of the directionality of lone pairs for proper adsorption of LiPS. The value of ELF can provide a quick estimate of bond strength.