PNNL

Abstract

The structure and phase stability of a series of lithiated titania polymorphs were determined using spin unrestricted density functional theory and the B3LYP exchange-correlation potential. These calculations were performed following the linear combination of atomic orbital approach. The lithium content, x, of the titania phases was varied from 0 to 1. Rutile and anatase were found to be the most stable polymorphs in the absence of lithium. Anatase and ramsdellite were calculated to become energetically favored over rutile upon lithium insertion. The hexagonal, spinel, and rocksalt polymorphs were predicted to have stabilities approaching that of rutile with increasing lithium content. At x=1, the hexagonal, spinel, rocksalt and rutile polymorphs showed essentially equivalent total energies. This prediction is consistent with the experimental observation that rutile electrodes, in particular those that consist of nanomaterials, undergo a phase transformation to the hexagonal, spinel, or rocksalt structure upon lithium insertion. In addition, a set of potential parameters was developed to model lithium insertion with a potential shell model. The potential model was found to give good agreement with the structure and energetics of the lithiated titania polymorphs, as determined with the ab initio calculations, at all lithium contents.