An Electrochemical Lithium Intercalation and Exfoliation Strategy on 2D Transition Metal Dichalcogenides for Phase Tuning and Energy Application

Description

Two-dimensional (2D) transition metal dichalcogenides (TMDs), a rising star in the post-graphene era, constitute a charming material library. Electrochemical lithium intercalation and exfoliation strategy (developed by our group) is a powerful tool for the scalable production of the atomically thin materials. Interestingly, semiconducting-tometallic phase transitions are often induced during the electrochemical lithium intercalation process, making the exfoliated final products (atomically thin TMDs) differ structurally and electronically from their starting counterparts (bulk crystals). Still, the in-depth phase transition mechanism remains to be clarified, and the correlation between phases and lithium intercalation amounts has not been investigated. These scientific issues will be addressed in this project, before delving into the energy application of the produced 2D TMDs.Firstly, the phase evolution and its in-depth mechanism are planned to be clarified with the help of the state-of-the-art in-situ and ex-situ characterization technologies. Insitu X-ray diffraction (XRD), Raman, and transmission electron microscope (TEM) will undertake the task of detecting the new-emerging phases of TMDs during lithium intercalation in real time and in operando. The Ex-situ high angle angular dark fieldscanning transmission electron microscopy (HAADF-STEM) is intended to be used to directly observe the lithium occupancy and the zigzag-chain arrangements of atoms in lithium intercalated TMDs.Secondly, MoS2 and TaS2 nanosheets are planned to be exfoliated from MoS2, Li0.1MoS2, Li0.3MoS2, Li0.5MoS2, Li0.8MoS2, Li1.1MoS2, and Li1.4MoS2, as well as, TaS2, Li0.1TaS2, Li0.2TaS2, Li0.5TaS2, Li0.7TaS2, and LiTaS2. Ex-situ multimodal characterizations will follow shortly, including HAADF-STEM, Raman, XRD, X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM), to investigate the phase, electronic structure, and morphology of the exfoliated TMDs nanosheets. By comparing the data with only lithium intercalated TMDs, we plan to uncover the underlying mechanism of the exfoliation process to the final properties of the exfoliated TMDs.Thirdly, supercapacitor electrodes will be fabricated using the exfoliated TMDs nanosheets with different phases (2H, 1T and 1T’) and different lithium intercalation amounts. Then, their supercapacitor performances will be investigated. On this basis, we will summarize how phases and lithium intercalation amounts influence the supercapacitor performance.The successful implementation of this proposal is expected to lead to a comprehensive understanding of lithium intercalation and exfoliation mechanism on TMDs. The results can provide us an effective guidance for tuning phase and lithium intercalation amounts of the exfoliated TMDs nanosheets on constructing TMDs based electrodes with superior electrochemical capacitance for energy application.