Fast Ionic Conductivity and Dielectric Properties of the Lithium Halide Spinels Li2MnCl4, Li2CdCl4, Li2MnBr4, and Li2CdBr4

Abstract The lithium bromide spinels Li 2 MnBr 4 and Li 2 CdBr 4 exhibit fast ionic conductivity in the solid state as the corresponding chloride spinels. The specific conductivities of the bromide spinels, however, are slightly smaller than those of the chlorides, e.g. for the cadmium compounds 0.11 and 0.26 Ω −1 cm −1 at 400°C, respectively. Even Li 2 MnCl 4‐−4x Br 4x solid solutions do not show higher conductivity than pure Li 2 MnCl 4 . The activation energies for conduction decrease at higher temperatures, e.g. from 60 to 33 kJ mol −1 for Li 2 MnBr 4 , caused by disorder of the cation sublattice at elevated temperatures. The non‐ideal dielectric behaviour of the lithium ion conducting compounds shown by a characteristic inclination of the spurs and skewness of the semicircles in the impedance diagrams can be correlated to both structure changes (disorder at elevated temperatures) and the different polarizability of the halide ions.