Mechanism of lithium ion mobility in solid electrolytes

Lithium ion transport in crystalline solid electrolytes is discussed with reference to a model system LISICON, Li_2+2xZn_1-xGeO₄. In LISICON, ionic conductivity is due to the presence of the interstitial Li⁺ ions which are not randomly distributed over sets of crystallographically identical sites but are incorporated within defect clusters. The structure of the solid consists of a mosaic of substructures, namely the lithium-rich defects and regions with the structure of stoichiometric Li₂ZnGeO₄. It is proposed that the interstitial Li⁺ ions are transported as an interstitial triple and that effectively the entire defect moves through the crystal. An explanation is also proposed for the curvature in the log s against 1/T plots for this electrolyte.