First Principles Modeling of the Thermodynamic and Kinetic Properties of Anatase LixTiO2 and the Ti-Al Alloy System With Dilute Vacancies.

TL;DRAbstract

We perform a comprehensive first-principles statistical mechanical study of the thermodynamic and kinetic properties of two separate materials systems with very different applications using a collection of reliable computational methods. Anatase TiO2 can be lithiated to LixTiO2 and has thus been a candidate material for Li-ion battery electrodes for quite some time. We establish that the experimentally observed step in the voltage vs lithium composition curve between x = 0.5 and 0.6 is due to Li ordering. Furthermore, we predict that full lithiation of anatase TiO2 is thermodynamically possible at positive voltages but that there is an enormous difference in Li diffusion coefficients in the dilute and fully lithiated forms of TiO2, providing an explanation for the limited capacity in large electrode particles. We also predict that Li diffusion in the ordered phase (Li0.5TiO2) is strictly one-dimensional. The TiO2 to Li0.5TiO2 phase transition has much in common with shape memory alloys

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