Computational Investigation of Structural, Optoelectronic, and Charge Transport Properties of Heteroatoms Doped Graphene Quantum Dot with Lithium and Potassium Polysulfides.

Abstract

In this study, we investigate the effect of heteroatom doping in graphene quantum dots (GQDs) in boosting the performance of metal-sulfur batteries using density functional theory (DFT) calculations. The properties, such as highest occupied and lowest unoccupied molecular orbits levels, absorption spectra, fundamental bandgap, adsorption energies, density of states, and charge transport properties of GQDs, heteroatom-doped GQDs, S₈, Li₂S_x (x = 2, 4, 6, and 8), and K₂S_x (x = 2, 4, 6, and 8), are compared to evaluate the best dopant in the carbon matrix. Our results show that the heteroatom-doped systems have a lower bandgap and, therefore, better conductivity. Further, based on adsorption energy calculations, we find that Li₂S₈ and K₂S₈ exhibit strong interaction with P- and S-doped GQDs, and thus, heteroatom doping can help to lower the shuttle effect. In addition, electron mobilities in N-, P-, and S-doped GQDs are larger than in the GQDs. The detailed analysis suggests that P and S are better dopants owing to their catalytic behavior toward soluble polysulfide apart from increasing the conductivity. This study can be helpful for the design and development of an efficient cathode matrix for lithium and potassium sulfur batteries.