| Abstract
| - By first-principles calculations, we obtain a better understanding of the unusual layered phases obtained upon Li deintercalation from O2-LiCoO2, namely, T#2 (we predict that Li ions occupy two tetrahedral sites) and O6. We also predict ordered compounds to be stable at room temperature. The driving forces of the phase transformations are discussed.
- A first-principles investigation of the phase stability in the O2-LiCoO2 system is performedto better understand the unusual layered phases obtained upon Li deintercalation (i.e., T#2and O6). First-principles pseudopotential calculations within the local density approximationand thermodynamic models extracted from these calculations both show that two tetrahedralsites for the Li ions need to be considered in the T#2 structure for qualitative agreementwith experiment to be obtained. Only when both tetrahedral sites in T#2 are considered isthe experimentally observed two-phase O2/T#2 region predicted. This indicates that thisstructural phase transformation is induced by enhanced configurational entropy in the T#2phase and not by a metal−insulator transition as was previously proposed. We also predictthat two ordered compounds are stable at room temperature: Li1/4CoO2 in the O2 structureand Li1/3CoO2 in the O6 structure. We show that the formation of the O6 phase is not relatedto Li staging.
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