Minsheng Lei

Ab initio studies on atomic and electronic structures of black phosphorus

The atomic and electronic properties of black phosphorus (BP), which has been recently shown to have potential application as anode material for lithium ion batteries, are studied via ab initio calculations. The calculations reveal that the interlayer interaction in BP is Van der Waals Keesom force, which is critical to the formation of the layered structure. Interestingly, we also found that the small band gap of bulk BP (0.19 eV) when compared with that of single layer BP (0.75 eV) is partly because of the interlayer Van der Waals interaction in BP. The change in a materials band structure because of Van der Waals interaction is rarely reported in literature.

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.