Heterointerface Effects on Lithium-Induced Phase Transitions in Intercalated MoS.

The intercalation-induced phase transition of MoS from the semiconducting 2H to the semimetallic 1T' phase has been studied in detail for nearly a decade; however, the effects of a heterointerface between MoS and other two-dimensional (2D) crystals on the phase transition have largely been overlooked. Here, calculations show that intercalating Li at a MoS-hexagonal boron nitride (BN) interface stabilizes the 1T phase over the 2H phase of MoS by ∼100 mJ m , suggesting that encapsulating MoS with BN may lower the electrochemical energy needed for the intercalation-induced phase transition. However, Raman spectroscopy of BN-MoS-BN heterostructures during the electrochemical intercalation of Li shows that the phase transition occurs at the same applied voltage for the heterostructure as for bare MoS. We hypothesize that the predicted thermodynamic stabilization of the 1T'-MoS-BN interface is counteracted by an energy barrier to the phase transition imposed by the steric hindrance of the heterointerface. The phase transition occurs at lower applied voltages upon heating the heterostructure, which supports our hypothesis. Our study highlights that interfacial effects of 2D heterostructures can go beyond modulating electrical properties and can modify electrochemical and phase transition behaviors.