ELECTROCHEMICAL INTERCALATION OF SODIUM INTO PBNBS3 AND PBNB2S5 MISFIT LAYER COMPOUNDS

Sodium intercalation into "PbNbS3" and "PbNb2S5" was studied in Na/NaClO4-propylene carbonate/sulfide electrochemical cells. The discharge curve for PbNbS3 showed an abrupt decrease in voltage at the first steps of the process, which is indicative of decomposition of the sulfide. For PbNb2S5, the discharge curve was analogous to that obtained by lithium intercalation and showed an apparent plateau between 0.05 and 0.30 F/mol. The X-ray and electron diffraction data showed that the misfit structure is maintained throughout intercalation. The unit cell parameter c increased gradually with Na-content. The initial value of 35.64 angstrom reaches a maximum value of 37.40 angstrom. This change is smaller than that observed in Na-intercalated NbS2, as a result of the changes induced in the PbS-NbS2 and NbS2-NbS2 gaps and the presence of sodium in octahedrally coordinated sites between consecutive NbS2 layers. For sodium contents greater than 0.9 atoms per mol, the misfit layer structure becomes unstable although significant changes are not observed in the cell voltage for this compound.