Understanding the modulation effect and surface chemistry in a heteroatom incorporated graphene-like matrix toward high-rate lithium–sulfur batteries

Abstract

The underlying interface effects of sulfur hosts/polysulfides at the molecular level are of great significance to achieve advanced lithium–sulfur batteries. Herein, we systematically study the polysulfide-binding ability and the decomposition energy barrier of Li₂S enabled by different kinds of nitrogen (pyridinic N, pyrrolic N and graphitic N) and phosphorus (P–O, PO and graphitic P) doping and decipher their inherent modulation effect. The doping process helps in forming a graphene-like structure and increases the micropores/mesopores, which can expose more active sites to come into contact with polysulfides. First-principles calculations reveal that the PO possesses the highest binding energies with polysulfides due to the weakening of the chemical bonds. Besides, PO as a promoter is beneficial for the free diffusion of lithium ions, and the pyridinic N and pyrrolic N can greatly reduce the kinetic barrier and catalyze the polysulfide conversion. The synergetic effects of nitrogen and phosphorus as bifunctional active centers help in achieving an in situ adsorption–diffusion–conversion process of polysulfides. Benefiting from these features, the graphene-like network achieves superior rate capability (a high reversible capacity of 954 mA h g⁻¹ at 2C) and long-term stability (an ultralow degradation rate of 0.009% around 800 cycles at 5C). Even at a high sulfur loading of 5.6 mg cm⁻², the cell can deliver an areal capacity of 4.6 mA h cm⁻² at 0.2C.