Abstract:

Based on the high theoretical lithium storage capacity of molybdenum disulfide (MoS₂) and the good conductivity of graphene, a curly lamellar MoS₂/reduced graphene oxide (RGO) composite was successfully prepared by a one-step hydrothermal method. The structure, morphology, and composition of the MoS₂/RGO composite were characterized using an X-ray diffractometer, scanning electron microscope, X-ray energy spectrometer, and Raman spectrometer. The most stable adsorption position of lithium-ion, charge density, charge density difference, density of states, and diffusion energy barrier of MoS₂ and MoS₂/RGO models were calculated by first-principles. Results show that the MoS₂/RGO composite maintains a high discharge specific capacity of more than 800 mAh/g in the first 70 charge and discharge cycles. After 100 cycles, the discharge specific capacity of the MoS₂/RGO composite is 515.3 mAh/g, which is significantly higher than that of MoS₂ (170.8 mAh/g). Simultaneously, the composite material shows a better rate of performance than MoS₂. When the current density is back to 100 mA/g after the 1000 mA/g high current density cycle, the MoS₂/RGO composite still maintains a high discharge specific capacity (941.2 mAh/g). The first-principles calculation results show that the charge near the Mo atom of MoS₂ decreases, and the whole density of states of the MoS₂/RGO composite is enhanced due to the action of graphene, making it easier for electrons in the valence band to migrate to the conduction band. Furthermore, compared with MoS₂, the low diffusion energy barrier (0.25 eV) of MoS₂/RGO makes it easier for lithium ions to diffuse. Therefore, it explains why the MoS₂/RGO composite has a better electrochemical performance than MoS₂ with the effect of graphene.

Key words: hydrothermal preparation, MoS₂/RGO composite, electrochemical performance, first-principles calculation