Density Functional Theory Study of Lithiation and Sodiation in Sb2S3 and Sb2Se3 Anode Accompanying by S/Se Redox

Abstract

Density functional theory simulation has been performed to illuminate the mechanism of lithiation and sodiation in Sb2S3 and Sb2Se3 anodes which is accompanied by anionic S/Se redox. The lithiation and sodiation of Sb2S3 and Sb2Se3 is comprised of two steps, (a) conversion and (b) alloying -dealloying. During conversion Sb and alkaline (Li/Na) chalcogenides are formed. Voltages during the conversion reaction of lithiation and sodiation were ∼1.6 and ∼1.25 V, respectively, for both Sb2S3 and Sb2Se3. Comparison of X-ray absorption near edge spectroscopy imaging of S/Se as present in pristine chalcogenides and A2S/Se with A = Li/Na reflects the presence of S/Se redox, which is further confirmed by electronic charge density analysis. Sb acts as an active center for the second step alloying-dealloying reaction. The formation of alloy mainly occurs via formation of Li3Sb and Na3Sb, which exhibits redox peaks at 1.025 V for lithiation and 0.686 V for sodiation. As reported in earlier reports, the redox peak, at 0.95 V is found to appear due to the formation of alloy NaSb.