KINETICS OF INTERCALATION OF LITHIUM AND SODIUM INTO (PBS)1.14(NBS2)2

The electrochemical and transport properties of the intercalation of Li and Na into (PbS)1.14-(NbS2)2, a misfit layer compound, have been investigated. The open-circuit voltage (OCV) of the lithium cell gradually decreases with increasing lithium content, while the OCV of Nax(PbS)1.14-(NbS2)2 shows the appearance of a voltage plateau in the range of composition 0.1 < x < 0.25. This different behavior has been correlated with the chemical diffusion coefficients obtained by a long-pulse galvanostatic technique. While the chemical diffusivity of lithium increased with composition and had a maximum of approximately 1.3 X 10(-9) cm2 s-1 for composition 0.4 < x < 0.5, the diffusion coefficients of Na+ were found to decrease slowly in the range 0.05 < x < 0.2, where the voltage-composition curve showed a two-phase region supported by the related X-ray data. On the other hand, the standard free energies of intercalation for sodium intercalates are less negative than those found for the respective lithium intercalated compounds.