Heterointerface Control over Lithium-Induced Phase Transitions in MoS₂ Nanosheets: Implications for Nanoscaled Energy Materials

Phase transitions of two-dimensional nanomaterials and their heterostructures enable many applications including electrochemical energy storage, catalysis, and memory; however, the nucleation pathways by which these transitions proceed remain underexplored, prohibiting engineering control for these applications. Here, we demonstrate that the lithium intercalation-induced 2H-1T′ phase transition in MoS2 nanosheets proceeds via nucleation of the 1T′ phase at an atomically thin heterointerface by monitoring the phase transition of MoS2/graphene and MoS2/hexagonal boron nitride (hBN) heterostructures with Raman spectroscopy in situ during intercalation. We observe that graphene–MoS2 heterointerfaces require an increase of 0.8 V in applied electrochemical potential to nucleate the 1T′ phase in MoS2 as compared to hBN–MoS2 heterointerfaces. The increased nucleation barrier at graphene–MoS2 heterointerfaces is due to the reduced charge transfer from lithium to MoS2 at the heterointerface as lithium also dopes graphene based on ab initio calculations. Furthermore, we show that the growth of the 1T′ domain propagates along the heterointerface rather than through the interior of MoS2. Our results provide the first experimental observations of the heterogeneous nucleation and growth of intercalation-induced phase transitions in two-dimensional nanomaterials and heterointerface effects on their phase transitions. These insights have implications for the design of energy technologies and devices that rely upon the phase stability of nanostructured materials.