Lithium-induced intralayer rearrangement of molybdenum disulfide: Effect of graphene coating

Nanoscale composites consisting of molybdenum disulfide and graphene (MoS2/graphene) are promising anode materials for lithium-ion batteries. In this work, to gain insight into the role of graphene coating in the interaction of lithium with MoS2, we used in situ X-ray photoelectron spectroscopy (XPS) experiments. The deposition of lithium was carried out in a high vacuum simultaneously on the surface of polycrystalline MoS2 and MoS2 coated with a few-layer graphene. The XPS Mo 3d and S 2p spectra of lithiated samples exhibited the appearance of low-energy components assigned to Mo-Mo bonds and weakened S-Mo bonds according to the density functional theory calculations. Such an atomic rearrangement in the MoS2 layer was much more significant for MoS2/graphene due to excess lithium in the interface. Annealing of the samples at 500 C revealed that the lithium-induced intralayer MoS2 rearrangement is irreversible despite the removal of lithium. Moreover, at 800 C, the rearranged MoS2 regions containing the residual lithium decomposed to form metallic molybdenum and Li2S2. This finding can help to understand the processes occurring in MoS2/graphene electrodes and to develop advanced materials for efficient lithium-ion batteries.