REDOX POTENTIALS AND DIFFUSION OF LITHIUM IN LAMELLAR COMPOUNDS

Abstract

Themodynamic and dynamic properties of intercalation products of lithium into MoS2 are strongly determined by the coordination of lithium in the interlaminar spaces. Lithium redox potentials as well as lithium diffusion coefficients in MoS2 pure, exfoliated, as well as in compounds where lithium is co-intercalated with the polymeric electron pair donors, poly(ethylene oxide) and poly-acrylonitrile, and discrete species, OH− ions and secondary amines, were analyzed comparatively. Reduction potentials in pure or exfoliated MoS2 are always much lower than those observed in lithium-donor co-intercalates. Thus, donors appear to effectively stabilize higher lithium oxidation states. The donors also influence lithium migration properties, with lithium diffusion coefficients in general higher than in pure MoS2. Lithium diffusion activation energy in pure MoS2 is constant in a relatively large lithium concentration range, while for co-intercalates it often depends on lithium intercalation degree. These more complex diffusion mechanisms probably arise from changes in the donor conformation in the interlaminar spaces, which affect the lithium first coordination sphere.