Phase transitions and diffusion kinetics during Mg2+- and Li+-ion insertions into the Mo6S8 chevrel phase compound studied by PITT

Abstract

Careful potentiostatic intermittent titrations (PITT) were performed in order to study Li+- and Mg2+-ion insertions into the Mo6S8 chevrel phase compound. Potential dependences of equilibrium and dynamic characteristics of the insertion processes, such as the differential intercalation capacitance, Cdif, the chemical diffusion coefficient, D, and the specific ionic conductivity, κ, were measured and interpreted in terms of lattice-gas models with highly attractive interactions between the inserted ions. Li-ion conductivity of the slightly intercalated chevrel phase is much higher than that of Mg-ions, which can be attributed to a higher charge density of the latter ion and to its higher polarization effect on the S8 anions’ lattice of the host material. Some crystallographic arguments related to the low mobility of the Mg-ion on the one hand, and the extremely high mobility of most of the divalent d-metal cations in the Mo6S8 chevrel phase on the other hand, are discussed.