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

Density functional theory simulation has been performed to illuminate the mechanism of lithiation and sodiation in Sb 2 S 3 and Sb 2 Se 3 anodes which is accompanied by anionic S/Se redox. The lithiation and sodiation of Sb 2 S 3 and Sb 2 Se 3 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 Sb 2 S 3 and Sb 2 Se 3. Comparison of X-ray absorption near edge spectroscopy imaging of S/Se as present in pristine chalcogenides and A 2 S/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 Li 3 Sb and Na 3 Sb, 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.