Influence of Oxygen–Sulfur Exchange on the Structural, Electronic, and Stability Properties of Alkali Hexastannates

Materials design plays a key role in predicting the properties of electrode materials for next-generation batteries. In this work, the structural, electronic, and stability properties of new potential anode materials with the stoichiometric formula A2Sn6X13 (A+ = Li+, Na+ or K+ X = O2- or S2-) are explored using density functional theory simulations. The effect of exchanging O2- with S2- in the A2Sn6O13 structures is reflected by an expansion of the lattice parameters, as well as the A-X distances, of the resulting A2Sn6S13 compounds. Electronic structure calculations confirm that all A2Sn6X13 structures have semiconductor characteristics. The band gap values are higher for A2Sn6O13 compared with their sulfur-containing counterparts. In particular, K2Sn6S13 has the lowest band gap of 0.49 eV, while K2Sn6O13 has the highest band gap of 3.08 eV. All the studied compounds are stable with respect to their decomposition products. The average cell voltages are 2.01, 1.93, and 1.87 V per A+/A intercalation for Li2Sn6S13, Na2Sn6S13, and K2Sn6S13, whereas their oxygen counterparts have higher values of up to 2.30 V per A+/A insertion.