Synthesis of MoS2 Thin Film by Chemical Vapor Deposition Method and Discharge Characteristics as a Cathode of the Lithium Secondary Battery

The discharge characteristics of MoS2 are much different from those of other layered materials. The discharge and charge characteristics strongly depend on the lithium diffusion in the van der Waals gap. In order to investigate the lith-ium diffusion, the cathode system was simplified by using the c-axis oriented MoS2 thin film prepared by chemical vapor deposition. The current-time transient in the course of the potentiostatic discharge was calculated assuming the finite one-dimensional diffusion of lithium. The diffusion coefficients were estimated from the comparison of the observed curve with the calculated one using the MoS~. film. In the electrode potential region from 3.6 to 1.5 V vs. Li/Li + of Li=MoS2, the observed current-time curve was in good agreement with the calculated one. The diffusion coefficient was estimated to be 5.8 • 10-1 ~ cm ~ s-L In the potential region from 1.5 to 1.2 V vs. Li/Li +, the simple diffusion model could not be applicable. The decrease in the crystallinity of Li=MoS2 occurred in this region. In the potential region from 1.2 to 0.9 V vs. Li/Li § the observed curve was in agreement with the calculated curve. From these facts, it can be seen that the structural degrada-tion occurs during the discharge and then the structural change is terminated when the electrode potential reached to 1.2 V. The diffusion coefficient was estimated to be 5.0 • 10-12 cm 2 s- ' which was larger than in the potential region from 3.6 to 1.5 V. As a cathode of secondary lithium battery, various mate-