Density functional theory study of SnSe2 as anode material for Mg ion battery application

Abstract

In this work we report, an effort to move beyond lithium ion battery, using density functional theory (DFT) approach to explore the possibility of SnSe2 as an anode material for Mg ion battery. Structural stability and changes in electronic structure on Mg insertion and related charge transfer mechanism has been examined. Results indicate three different types of reaction mechanism on Mg+2 addition to SnSe2. The possible reaction stages are; (a) Mg+2 intercalation in van der Waals gap of SnSe2 structure in the Sn–Se layers, (b) conversion reaction initiated in the semiconducting phase MgSe and metallic Sn, (c) alloying reaction occurring via formation of metallic alloy Mg2Sn. The estimated voltage for these three distinct reaction mechanisms are; (a) ∼1.1 V during Mg+2 intercalation, (b) 0.65 V during conversion reaction, (c) ∼0.26 V during alloying that sustains ultimately. The volume strain is minimal during intercalation (∼10.54%–13.38%) while maximum (∼253.3%–267.7%) during alloying-dealloying reaction. Formation of semiconducting MgSe phase causes loss of capacity during the first cycle operating within voltage window <1.5 V and it accounts for the irreversible capacity loss. The maximum achievable capacity is estimated to be ∼774.8 mAh/g while after first discharge it is likely to stabilize close to ∼640.7 mAh/g for alloying-dealloying reaction. Results indicate feasibility of Mg ion battery in near future.