ELECTROCHEMICAL LITHIUM INTERCALATION INTO MISFIT LAYER SULFIDES

Ternary sulfides of approximate formulas, PbVS3, PbTiS3, and PbTi2S5 and misfit layered structures were used as cathodes in lithium test cells. The discharge and OCV curves for PbVS, and PbTiS3 were consistent with the concomitant occurrence of pristine and isostructural lithiated phases at low discharge depths, which led to a short quasi-plateau below 0.5 Li/formula unit, which was particularly outstanding for the vanadium compound. Further discharge resulted in progressive amorphization of the lithiation product in an extended plateau that was preserved at higher discharge depths in the case of vanadium. For PbTi2S5, the presence of consecutive 1-T related TiS2 slabs in the structure allowed the formation Of a 105-angstrom phase, which can be described as stage III, with a HLiHCHHCHHC stacking unit. The co-occurrence of this phase and pristine PbTi2S5 resulted in an initial plateau below 0.3 F. The X-ray diffraction data obtained between 0.3 and 0.8 F suggest the presence of stage III and stage I lithiated phases. Above 0.8 F, stage I and amorphous products are involved that give rise to an extended plateau in the discharge curve.