The Mechanistic Insights into the 2H‐1T Phase Transition of MoS2 upon Alkali Metal Intercalation: From the Study of Dynamic Sodiation Processes of MoS2 Nanosheets

Phase transition in 2D MoS2 is an important issue in transition metal dichalcogenides. The mechanism of the phase transition is investigated extensively, while a comprehensive understanding of the mechanism remains to be elusive. The 2H to 1T phase transition of MoS2 can be induced by intercalation with alkali metals, associated with transformation of its electronic and structural orders. Here, by using in situ transmission electron microscopy, the electrochemical sodiation processes of MoS2 nanosheets are investigated. This paper points out an intermediate phase 2H‐Na0.25MoS2 with 2 × √3 superstructure. The phase transition occurs from 2H‐Na0.5MoS2 to 1T‐Na0.5MoS2, where the ratio of Mo3+ and Mo4+ is 1:1 and intervalence charge transfer (IVCT) between the two ions should not be neglected. Based on this viewpoint it is proposed that the IVCT plays an important role in the formation of the phase transition. The findings provide a new perspective on the mechanism of the phase transition, and help to better understand the phase transition mechanism of other transition metal dichalcogenides.