ELECTROCHEMICAL ALKALI-METAL INTERCALATION INTO (BIS)1.17(NBS2)2

Lithium and sodium electrochemical intercalation into the (BiS)1.17(NbS2)2 misfit layer compound was studied in A/AClO4(PC)/sulfide cells (A = Li, Na). The periodic length of the original compound (17.385 angstrom) is consistent with an NbS2-NbS2-BiS stacking sequence. This parameter increased by about 0.33 and 0.78 angstrom after 1 F/mol discharges of Li and Na cells, respectively. For both alkali metals, the potentiostatic discharge curve of the cells showed an initial decrease in voltage followed by subtle changes in the slope of the voltage-composition curve. Current versus voltage curves revealed three diffuse peaks ascribable able to lithium ordering in the interlayer space, while a single peak occurred for sodium at about 1.5 V. The chemical diffusion coefficients of Li are consistent with octahedral site occupancy. Na intercalation perturbed the structure heavily as shown by the low diffusion coefficients of sodium ions.