Chloride spinels: A new group of solid lithium electrolytes

The chloride spinels Li2MCl4 with M = Mg, Mn, Fe and Cd show very high lithium ionic conductivity in the solid state. The ionic conductivity in the compounds under investigation was established with the help of emf measurements. The specific conductivities measured by both frequency response analysis and the four probe ac method are 1.3 Ω−1 · cm−1 for Li2CdCl4, and about 0.9Ω−1 · cm−1 for Li2MnCl4, Li2MgCl4, and Li2FeCl4 at 773 K. There are several indications that the ternary chlorides become highly disordered at elevated temperatures. Thus the Arrhenius plots, i.e. In σ · T vs 1/T-curves, exhibit significant bends, the slopes below the transition temperature being considerably higher than those above.