Insight into the effects of gas molecules-adsorbed on 2D-FeS2: A DFT study

Abstract

Lithium-sulfur (Li-S) batteries are especially competitive in the energy sector due to their excellent performances, like preferable energy density and economic benefits. Studying the adsorption of gas molecules on electrode materials has potential engineering significance for Li-S batteries since they have a highly osmotic potential, which causes unavoidable damage to batteries. In this work, the adsorption phenomenon of common gas molecules (H₂O, N₂, H₂, CO₂, and O₂) on the two-dimensional pyrite (2D-FeS₂) cathode material surface, as well as the effects on the electronic and electrochemical properties, were investigated by the first-principles calculations. The adsorption capabilities were estimated by adsorption energy and Mulliken population analysis. Simulation results demonstrated that whole adsorption energies were less than -1.0 eV and larger than -0.6 eV, which shows a physisorption nature. Among them, the O-S bond of O₂/2D-FeS₂ has the strongest strength. Electronic structure calculations suggested that 2D-FeS₂ maintained good conductivity after gas molecules were adsorbed, achieving efficient transfer between electron, lithium, and sulfur intermediates. Additionally, ab initio molecular dynamics (AIMD) simulations showed that Li⁺ exhibits excellent diffusion performance and low activation energy at different temperatures. 2D-FeS₂ still has a stable electrochemical working window (1.87 ∼ 2.47 V), while the theoretical open current voltage is damaged by gas molecule adsorption. Consequently, this work theoretically reveals the effect of gas molecules on the cathode materials for Li-S batteries, which has guide meaning for engineering.