Li+ intercalation chemistry on 2D transition metal dichalcogenides towards phase evolution, scalable production and application

Abstract Li+ intercalation chemistry is a powerful tool to induce phase transitions in transition metal dichalcogenides (TMDs), but only the transition of 2H-to-1T/1T’ in group Ⅵ TMDs (MoS2 and WS2) is well-known and widely explored for applications in areas such as transistors, memristor, catalysis, and batteries. Here, we develop a fully documented landscapes of phase evolution in group IV-Ⅵ TMDs induced by electrochemical Li+ intercalation through in-situ X-ray diffraction (XRD) and Raman techniques. We found emerging structural phase evolutions never been noticed before, including 1T-to-1T (transition-free) in group IV TMDs (TiS2 and ZrS2), 2H-to-3R in group Ⅴ TMDs (NbS2), as well as 1T-to-2H in group Ⅴ TMDs (VS2 and TaS2). Theoretical calculations uncoverd the crucial role played by lithium intercalation in facilitating electron transfer from the s orbital of lithium to the d orbital of the transition metal center and clarified the reasons of the difference of phase transitions for different families of TMDs. Furthermore, we discovered that phase transitions also appear in the subsequent exfoliation process for scalable preparation of TMD atomically thin sheets, embodying 1T-to-1T (transition-free) in TiS2, 1T-to-amorphous in ZrS2, 3R-to-H in NbS2, 2H-to-1T in VS2 and TaS2. Our developed Li+ intercalation chemistry enrich the phase transition nanotechnology, which facilitates not only the understanding of the mechanism of phase transition but also its control, opening up new possibilities for phase-dependent TMD-based nanoelectronic, photonic, and thermoelectric devices. As a proof-of-concept application, we developed a thermoelectric device using of our exfoliated TiS2 nanosheets, achieving a maximum power density of 458.6 W∙m−2 at a 53 K temperature difference.