Abstract
The thermodynamic and structural properties of Li x TiO 2 spinel are investigated by means of a cluster expansion based on pseudopotential ground state energy calculations in the Generalized Gradient approximation (GGA). The cluster expansion enables a Monte Carlo simulation of configurational thermodynamics, giving the Li configurations, chemical potential and the insertion potential as function of Li composition at 300 K. For 1/2 < x < 1Li x TiO 2 we find a two-phase region, consistent with what is found experimentally. The two coexisting phases differ in the sites occupied by Li: in Li 1/2TiO 2 and LiTiO 2 Li occupies the crystallographic 8a and 16c sites, respectively. This site occupation and the changes in the unit cell dimensions compare well with X-ray and neutron diffraction experiments. For x < 1/2 in Li x TiO 2 solid solution behavior is found and Li extraction can only occur at higher potentials. The potential step at Li 1/2TiO 2 is calculated to be 1.4 V, in good agreement with experiment, but considerably higher than in the comparable Co and Mn-spinel.
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