First-Principles Calculations of Absorption Properties of Cs2F5Li3 to Li2S

Abstract:

Lithium-sulfur batteries (LSBs) have extremely high theoretical energy density and low-cost cathode materials. However, the recycling of LSBs will produce polysulfides (LiPSs), which has a serious “shuttle effect”, resulting in highly polarized batteries, impaired battery performance, and even safety issues, and making the application of LSBs still extremely challenging. In this work, the binding energy of was used to discuss the absorption capacity of Cs₂F₅Li₃ to Li₂S, i.e., the ability to inhibit its “shuttle effect”. Based on the first-principles method of density functional theory, Cs₂F₅Li₃ and Li₂S were simulated by CASTEP software, and the binding energy of Cs₂F₅Li₃ to Li₂S is –2.53 eV. In order to explore the mechanism of adsorption, the basic properties, electronic structures, and charge transfer of Cs₂F₅Li₃ and Li₂S bulk phases, Li₂S(100), Cs₂F₅Li₃(001), and Cs₂F₅Li₃(001)-Li₂S(100) were used for analysis. The results show that the binding energy is provided by the ionic bond between F 2p and Li 1s2s as well as S 3p and Li 1s2s, the covalent bond between S 3p and F 2p, and the relaxation exchange energy of the bonds in the system. After the section, Cs₂F₅Li₃(001) has stronger chemical activity than Cs₂F₅Li₃, and Li₂S crystal changes from semiconductor property to metallic property. The metallic property of Cs₂F₅Li₃(001)-Li₂S(100) system improves, electrical conductivity is stronger, and photoelectric effect is stronger than that of Cs₂F₅Li₃(001). The adsorption energy calculation results show that Cs₂F₅Li₃ can inhibit the “shuttle effect” caused by the diffusion of Li₂S, which is conducive to alleviate the problems such as slow reaction kinetics, low activity, and reduced battery capacity caused by Li₂S, and it has a strong theoretical reference value for improving the performance of LSBs.