Density functional theory and experimental study of multi-step lithiation in SnS2 anode

We report in this work, using density functional theory, the possibility of multi-step lithiation in SnS 2 to understand charge storage mechanism, characteristic response as an electrode, and redox potential arising as a result of electrochemical charge transfer. The simulation results have indicated four stages of lithiation comprising intercalation, disordering, conversion, and alloying reactions occurring in the potential window range: 0–2.0 V. The multi-step lithiation mechanisms are (a) Li intercalation in layered SnS 2 , (b) a disordering reaction that converts layered hexagonal LiSnS 2 into cationically disordered cubic rock-salt LiSnS 2 , (c) conversion reaction accompanied by formation of an insulating Li 2 S phase and metal Sn, and (d) formation of Li 4.4 Sn alloy due to optimal lithiation of Sn metal due to alloying action. The estimated redox voltage corresponding to intercalation, conversion, and alloying reaction are (a) 1.72 V, (b) 1.56 V, and (c) 0.477 V, respectively. The simulation results so obtained has been validated through experimental analysis of coin cell results with configuration; Li || LiPF 6 /separator || SnS 2 . The experimental results of cyclic voltammetry, charge–discharge response, and electrochemical impedance spectrum agree well with the simulation results confirming that stable alloying-dealloying reaction prevails ultimately.