First-principles study of the discharge electrochemical and catalytic performance of the sulfur cathode host Fe 0.875 M 0.125 S 2 (M = Ti, V).

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 0.875 M 0.125 S 2 (M = Ti, V), as the sulfur cathode host, enhances the Li-S redox chemistry. FeS 2 with Pa 3̄ is transformed into Li 2 FeS 2 with P 3̄ m 1 after discharge. The structure changes and physicochemical properties during Fe 0.875 M 0.125 S 2 discharge process are further investigated to screen out the sulfur cathode host materials with the best comprehensive properties. The discharge structure of Fe 0.875 M 0.125 S 2 is verified by the thermodynamic stability of Li-deficient phases, voltage and capacity based on Monte Carlo methods. Fe 0.875 M 0.125 S 2 with Pa 3̄ is transformed into Li 2 Fe 0.875 M 0.125 S 2 with P 3̄ m 1 after discharge. Using the first-principles calculations, the physicochemical properties of Li 2 Fe 0.875 M 0.125 S 2 are systematically investigated, including the formation energy, voltage, theoretical capacity, electrical conductivity, Li + diffusion, catalytic performance and Li 2 S oxidation decomposition. The average redox voltage of Li 2 Fe 0.875 V 0.125 S 2 is higher than that of Li 2 Fe 0.875 Ti 0.125 S 2 . Li 2 Fe 0.875 M 0.125 S 2 shows metallic properties. Li 2 Fe 0.875 V 0.125 S 2 is more beneficial to the reduction reaction of Li 2 S 2 and Li 2 S oxidation decomposition. Fe 0.875 V 0.125 S 2 has more potential as the sulfur cathode host than Fe 0.875 Ti 0.125 S 2 in LSBs. A new strategy for the selection of the sulfur cathode host material for LSBs is provided by this work.