Double-active-site enables 2D B2S and B2S3 catalyst with suppressed shuttle effect and improved polysulfides redox kinetics in lithium-sulfur batteries: A first-principles study

Abstract

The sluggish transformation kinetics of lithium polysulfides (LiPSs) and the notorious shuttle effect induced by the emergence of highly soluble LiPSs have become the main obstacles preventing the application of lithium-sulfur batteries. The development of bifunctional catalysts capable of accelerating the LiPSs redox kinetics and anchoring these soluble LiPSs is highly desirable for achieving improved cycling performance and Coulombic efficiency. Herein, a two-dimensional B2S/B2S3 catalyst with atomically dispersed boron and sulfur sites was investigated as a potential additive to boost the anchoring of soluble LiPSs and the subsequent LiPSs transformation reaction. Based on first-principles calculations, we demonstrated that the adsorption strengths of soluble LiPSs on B2S/B2S3 monolayers are neither strong nor weak. This effectively inhibits the dissolution of LiPSs while retaining their structural integrity. Importantly, B2S/B2S3 exhibits remarkable catalytic activity toward the liquid-solid (Li2S4 to Li2S2) and solid-solid (Li2S2 to Li2S) reactions in the discharging process as well as the decomposition of Li2S in the charging process. This is crucial for achieving improved rate performance. Moreover, a high Li-ion mass transfer efficiency on B2S and B2S3 was achieved with Ebar values of 0.43 and 0.41 eV, which is beneficial for reducing diffusion-dependent polarization issues. Our results provide an alternative route for developing advanced sulfur cathode catalysts with a suppressed shuttle effect and desirable rate performance.