Ab initio studies on Li4+xTi5O12 compounds as anode materials for lithium-ion batteries.

The structural and electronic properties of Li(4+) (x)Ti(5)O(12) compounds (with 0<or=x<or=6)-to be used as anode materials for lithium-ion batteries-are studied by means of first principles calculations. The results suggest that Li(4)Ti(5)O(12) can be lithiated to the state Li(8.5)Ti(5)O(12), which provides a theoretical capacity that is about 1.5 times higher than that of the compound lithiated to Li(7)Ti(5)O(12). Further insertion of lithium species into the Li(8.5)Ti(5)O(12) lattice results in a clear structural distortion. The small lattice expansion observed upon lithium insertion (about 0.4 % for the lithiated material Li(8.5)Ti(5)O(12)) and the retained [Li(1)Ti(5)](16d)O(12) framework indicate that the insertion/extraction process is reversible. Furthermore, the predicted intercalation potentials are 1.48 and 0.05 V (vs Li/Li(+)) for the Li(4)Ti(5)O(12)/Li(7)Ti(5)O(12) and Li(7)Ti(5)O(12)/Li(8.5)Ti(5)O(12) composition ranges, respectively. Electronic-structure analysis shows that the lithiated states Li(4+x)Ti(5)O(12) are metallic, which is indicative of good electronic-conduction properties.