Janus transition metal dichalcogenides with unique physical properties have recently attracted increasing research interest for their energy and catalytic applications. In this paper, we investigate the lithiation behavior of a square phase Janus MoSSe monolayer (1S-MoSSe) using first-principles calculations. Computational results show that a single Li atom energetically prefers to adsorb on the central site of the octagonal ring (O site) and on the S-layer side of 1S-MoSSe. The predicted energy barriers for Li diffusion are surface dependent and in the range of 0.33 to 0.51 eV, indicating the acceptable Li migration kinetics on 1S-MoSSe in comparison with other 2D TMD materials. Further thermodynamic analysis demonstrates that Li adsorption on 1S-MoSSe is energetically stable up to a Li concentration of x = 1.0, above which the lithiation process becomes unstable with a negative charging potential. Phonon calculations also confirm that Li adsorption (0.25 ≤ x ≤ 0.75) results in the lattice distortion of 1S-MoSSe in order to suppress the structural instability of the lithiated monolayer 1S-Li x MoSSe with imaginary phonon frequencies. The less symmetric nature of 1S-MoSSe is believed to destabilize Li adsorption at much smaller x than 1H-MoSSe does, regardless of the higher dipole moment of 1S-MoSSe. This computational study provides a fundamental understanding of the electrochemical performance of 1S-MoSSe, as well as useful insight into the material design of Janus TMD anodes for Li-ion batteries.
This journal is © The Royal Society of Chemistry.