Alkali-metal-intercalated transition metal disulfides: A thermodynamic model

Abstract

In the lithium-intercalated disulfides, Li x MS 2, where M = Ti, Ta, a nearly linear compositional variation of the lithium chemical potential is observed throughout the composition range 0 < x < 1.0. For most sodium-intercalated disulfides, chemical potential plateaus are observed between regions exhibiting linear variations of sodium chemical potential. Our thermodynamic model indicates that the two most important factors which determine the compositional variation of the alkali metal chemical potential are the interaction energy between intercalated alkali-metal atoms and the compositional variation of the electron chemical potential. Although these two factors determine the compositional variation of chemical potential in single-phase regions, the existence of two-phase regions in the concentration range x = 0−0.15 are influenced by the energy required to expand the interlayer gap and the configurational entropy.