Prediction of Li Intercalation and Battery Voltages in Layered vs. Cubic Li x CoO2

It is now possible to use a quantum‐mechanical electronic structure theory of solids and derive, completely from "first‐principles," the voltage of a battery based on intercalation reaction energetics. Using such techniques, we investigate the structural stability, intercalation energies, and battery voltages of the two observed ordered phases ("layered" and cubic) of . We perform calculations for not only fully lithiated , but also fully delithiated □ and partially delithiated . Our calculations demonstrate that removal of Li from the cubic phase results in movement of the Li atoms from their original octahedral sites to tetrahedral sites, forming a low‐energy spinel structure. The energetics of the spinel phase are shown to account for the observed marked differences in battery voltages between the cubic and layered phases of . A small energy barrier exists for Li motion between octahedral and tetrahedral sites, thus indicating the metastability of the high‐energy octahedral sites. Finally, we point out a possible pressure‐induced layered → cubic transition in .