Ab initio studies of Ti2S3 as a new cathode material for magnesium secondary batteries

Abstract

In this work, we use spin unpolarized van der Waals-corrected static for the comparative study of highly defective TiS2 with Ti2S3 stoichiometry and stoichiometric TiS2, a well-known compound studied experimentally. Our study predicts that Ti2S3 exhibits high theoretical capacity of up to 112 mA h/g, moderate stability, a high electronic conductivity (zero band gap for all magnesium contents), and 0.8–1.0 eV lower operating voltage due to less intense Ti3+/Ti2+ redox couple. The bond valence sum method analysis showed that Mg diffusion occurs through the hopping of Mg cations between the cavities in the form of cubes. In contrast, nudged elastic band method reveals the linear topology of the migration path. Although in Ti2S3 a huge contraction of the c parameter was found (up to 8.17% in comparison with TiS2), the migration barrier for Mg diffusion was found to be comparable to that of layered TiS2 (1.078–1.281 eV depending on Mg content). This can be explained by the lower partial atomic charge of Ti in Ti2S3, as well as rehybridization over higher amount of Ti atoms.