C9N4 and C2N6S3 monolayers as promising anchoring materials for lithium–sulfur batteries: weakening the shuttle effect via optimizing lithium bonds

Abstract

The notorious polysulfide shuttle effect is a crucial factor responsible for the degradation of Li-S batteries. A good way to suppress the shuttle effect is to effectively anchor dissoluble lithium polysulfides (LPSs, Li₂S_n) on appropriate substrates. Previous studies have revealed that Li of Li₂S_n is prone to interact with the N of N-containing materials to form Li–N bonds. In this work, by means of density functional theory (DFT) computations, we explored the possibility to form Li bonds on ten different N-containing monolayers, including BN, C₂N, C₂N₆S₃, C₉N₄, a covalent triazine framework (CTF), g-C₃N₄, p-C₃N₄, C₃N₅, S-N₂S, and T-N₂S, by examining the adsorption behavior of Li₂S_n (n = 1, 2, 3, 4, 6, 8) on these two-dimensional (2D) anchoring materials (AMs), and investigated the performance of the formed Li bonds (if any) in inhibiting the shuttle effect. By comparing and analyzing the nitrogen content, the N-containing pore size, charge transfer, and Li bonds, we found that the N content and N-containing pore size correlate with the number of Li bonds, and the formed Li–N bonds between LPSs and AMs correspond well with the adsorption energies of the LPSs. The C₉N₄ and C₂N₆S₃ monolayers were identified as promising AMs in Li-S batteries. From the view of Li bonds, this work provides guidelines for designing 2D N-containing materials as anchoring materials to reduce the shuttle effect in Li-S batteries, and thus improving the performance of Li-S batteries.