Vacancy effect on the structure and diffusion of a Li adatom on the 2D Janus MoSSe monolayer

Abstract Monolayer MoSSe is a polar two-dimensional (2D) material which has gained significant attention in the field of nanodevices, like Li-ion batteries, for its small Li-ion migration barrier and high theoretical capacity. In order to explore the effect of vacancy defects on its performance, we performed a comparative study on the structures and migration of the Li adatom on the Janus MoSSe monolayer, with and without vacancies, from first-principles calculations. We found that multi-Li adatoms always preferred to be dispersed on the top of the Mo atoms in the S layer for the perfect 2D MoSSe monolayer. However, they tended to cluster on the ones near the vacancy when the Se vacancy formed in the 2D MoSSe monolayer. This feature was further demonstrated when the migration of the Li adatom was taken into account in the 2D MoSSe monolayer with vacancy defects. Our previous research showed that a zigzag Se linear vacancy is easily formed in the 2D MoSSe monolayer, based on which a Li adatom was added on it in this study. It was found that the Li adatom far away from the vacancy easily migrated close to the vacancy, and the one close to the vacancy easily migrated along the zigzag Se linear vacancy. These results indicated that vacancy defects can control the distribution and migration path of Li adatoms and provides an important guid to design nanodevices with monolayer MoSSe.