  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 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.
