Phase Transition and Ionic Conductivity of the Spinel System Li2−2xMg1+xCl4

Recently, a new class of lithium ion conductors, Li2MCl4(M=Mg,Mn,Fe,Cd), has been reported by Lutz et al. (1) and Kanno et al.(2), which has a high ionic conductivity at moderate temperatures. The compound Li2MCl4 has been determined by the neutron diffraction method to have the inverse spinel structure(3); half of the lithium ions are tetrahedrally surrounded by chloride ions, and the other half of them, together with the M ions, are distributed statistically over the octahedral sites. Lutz et al. (4) found the reversible phase transition from the spinel structure to a cubic defect structure at a high temperature. Of these compounds, Li2CdCl4. has the highest conductivity of 0.35 Scm-1 at 400°C, the value of which is comparable or more than that of the high lithium ion conductors reported previously.