Considerable effort has been devoted in recent years to the development of practical, secondary lithium batteries using intercalation cathodes. One limitation of many of these batteries has been their relatively low power densities. Significant progress has been made towards alleviating this limitation in cells utilizing lithium-molybdenum disulfide technology.
Frequency response analysis has proven to be a powerful tool for use in studying rate limitation mechanisms in cells. For the lithium-molybdenum disulfide system as developed in this laboratory, we have found that diffusion-related contributions to cell impedance, and interfacial and resistive contributions to cell impedance, can be readily segregated by virtue of the fact that the diffusioncontrolled mechanisms dominate the low frequency end of the impedance spectra whereas the other mechanisms dominate the high frequency end.
In this paper we report on a study of rate limitations at the high end of the frequency spectrum in lithium-molybdenum disulfide cathodes. We have identified and quantified in these cathodes, using a transmission line model, impedance elements corresponding to electrolyte impedance, a cathode grain/electrolyte interface impedance, and a grain-to-grain contact impedance that includes both a resistive and a capacitive element.