First-principles study of the discharge electrochemical and catalytic performance of the sulfur cathode host Fe0.875M0.125S2 (M = Ti, V)

Abstract

Lithium–sulfur batteries (LSBs) are one of the most promising energy storage devices with high energy density. However, their application and commercialization are hampered by the slow Li–S redox chemistry. Fe_0.875M_0.125S₂ (M = Ti, V), as the sulfur cathode host, enhances the Li–S redox chemistry. FeS₂ with Pa is transformed into Li₂FeS₂ with Pm1 after discharge. The structure changes and physicochemical properties during Fe_0.875M_0.125S₂ discharge process are further investigated to screen out the sulfur cathode host materials with the best comprehensive properties. The discharge structure of Fe_0.875M_0.125S₂ is verified by the thermodynamic stability of Li-deficient phases, voltage and capacity based on Monte Carlo methods. Fe_0.875M_0.125S₂ with Pa is transformed into Li₂Fe_0.875M_0.125S₂ with Pm1 after discharge. Using the first-principles calculations, the physicochemical properties of Li₂Fe_0.875M_0.125S₂ are systematically investigated, including the formation energy, voltage, theoretical capacity, electrical conductivity, Li⁺ diffusion, catalytic performance and Li₂S oxidation decomposition. The average redox voltage of Li₂Fe_0.875V_0.125S₂ is higher than that of Li₂Fe_0.875Ti_0.125S₂. Li₂Fe_0.875M_0.125S₂ shows metallic properties. Li₂Fe_0.875V_0.125S₂ is more beneficial to the reduction reaction of Li₂S₂ and Li₂S oxidation decomposition. Fe_0.875V_0.125S₂ has more potential as the sulfur cathode host than Fe_0.875Ti_0.125S₂ in LSBs. A new strategy for the selection of the sulfur cathode host material for LSBs is provided by this work.