Transport and Charge Carrier Chemistry in Lithium Oxide

Lithium oxide (Li 2 O) is a highly relevant material for battery applications, and as a binary antifluorite compound of first-row elements, it is equally interesting for basic science. This work investigates the behavior of ionic and electronic charge carriers in Li 2 O. The predominantly ionic conductivity is shown to be well-explained by a defect chemical model based on Frenkel disorder, vacancy migration, and vacancy-dopant association. The enthalpies and entropies of these three processes are derived, and good agreement is seen to isostructural Li 2 S, SrF 2 , and BaF 2 . An upper bound is determined for the electronic conductivity of Li 2 O, which is very low. These results provide more reliable thermodynamic and kinetic parameters for future rigorous treatments of Li 2 O in batteries. For example, even under favorable doping conditions, the ionic conductivity of bulk crystalline Li 2 O (with no higher-dimensional defects or interfacial effects) is multiple orders of magnitude too slow to account for the resistance of typical solid-electrolyte interface (SEI) layers.