Suppressing Polysulfides Shuttling and Promoting Sulfur Utilization via Transition Metal and Nitrogen Co-Doping on Graphdiyne Cathodes of Lithium-Sulfur Batteries: A First-Principles Modeling

While lithium-sulfur (Li-S) batteries are considered the next-generation energy storage devices, several issues inhibit their commercialization, including poor conductivity, shuttling of lithium polysulfides (LiPSs), and sluggish decomposition of small LiPSs. Here, we illustrate through first-principles modeling that doping graphdiyne (GDY) with transition metal (Co, Fe) and nitrogen (TM-N) effectively suppresses the shuttle effect and enhances sulfur utilization by promoting dissociation of small LiPSs. We find that the TM-N doping provides additional electrons to the substrate, which could improve the redox activity of the substrates. The additional electrons also improve charge transfer between the substrate and adsorbate that enhances the LiPS adsorption. Electronic structure analysis reveals that the strong interactions originate from the formation of TM-S bonds and electrostatic attractions between Li and N. Such strong adsorptions prevail in the interaction between the LiPSs and electrolyte molecules; hence, the doped GDY could effectively prevent the dissolution of LiPSs and inhibit the shuttle effect. Moreover, the doped GDY substrates exhibit small barriers of Li–S and Li–N bond breaking that facilitate the decomposition of small LiPSs. This implies that TM-N-doped GDY promotes kinetics of LiPS transformation, which increases sulfur utilization and diminishes capacity fading upon charge–discharge cycles. From the computational viewpoints, the TM-N-doped GDY substrates are considered promising cathodes of Li-S batteries. This work serves as a useful guide to rationally design high-performance two-dimensional (2D) carbon-based cathode materials for Li-S batteries.