Tuning the critical Li intercalation concentrations for MoX$_2$ bilayer phase transitions

TL;DR

This study investigates how Li intercalation induces phase transitions in MoX$_2$ bilayers, revealing how the critical Li concentration for phase change depends on the chalcogen atom's mass and analyzing electronic conductivity changes.

Contribution

It provides new insights into the relationship between chalcogen mass, Li concentration, and phase stability in MoX$_2$ bilayers using first-principles and machine learning methods.

Findings

H phase is more stable at low Li concentrations for all X

Critical Li concentration for phase transition decreases with increasing X mass

Electronic conductivity increases with Li concentration but no jump at phase transition

Abstract

Transition metal dichalcogenides (TMDs), such as MoS$_2$, are known to undergo a structural phase transformation as well as a change in the electronic conductivity upon Li intercalation. These properties make them candidates for charge-tunable ion-insertion materials that could be used in electro-chemical devices. In this work we study the phase stability and electronic structure of H and T$^\prime$ Li-intercalated MoX$_2$ bilayers with X=S, Se, or Te. Using first-principles calculations in combination with classical and machine learning modeling approaches, we find that the H phase is more stable at low Li concentration for all X, and the critical Li concentration at which the T$^\prime\to$H transition occurs decreases with increasing mass of X. Furthermore the relative free energy of the two phases becomes less sensitive to Li insertion with increasing atomic mass of the chalcogen atom X. While the electronic conductivity increases with increasing ion concentration at low concentrations, we do not observe a (positive) conductivity jump at the phase transition from H to T$^\prime$.