Heterointerface Effects on Lithium-Induced Phase Transitions in Intercalated MoS₂

The intercalation-induced phase transition of MoS₂ 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 MoS₂ and other two-dimensional (2D) crystals on the phase transition have largely been overlooked. Here, ab initio calculations show that intercalating Li at a MoS₂-hexagonal boron nitride (hBN) interface stabilizes the 1T phase over the 2H phase of MoS₂ by ∼100 mJ m ^-2, suggesting that encapsulating MoS₂ with hBN may lower the electrochemical energy needed for the intercalation-induced phase transition. However, in situ Raman spectroscopy of hBN-MoS₂-hBN heterostructures during the electrochemical intercalation of Li⁺ shows that the phase transition occurs at the same applied voltage for the heterostructure as for bare MoS₂. We hypothesize that the predicted thermodynamic stabilization of the 1T'-MoS₂-hBN 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.