C.H. Hu

Structural properties and energetics of Li2FeSiO4 polymorphs and their delithiated products from first-principles

Structural properties, thermodynamic stability and delithiation process for Li(2)FeSiO(4) polymorphs are investigated by using density functional theory (DFT) within the DFT + U framework. Three Li(2)FeSiO(4) polymorphs crystallizing in space group Pmn2(1), P2(1)/n, and Pmnb have been considered. The investigations demonstrate that the strong Si-O bonds remain almost unchanged during the lithiation-delithiation process for all the polymorphs, which contribute significantly to the structural stability. On the other hand, the differences in local environment around FeO(4) tetrahedra will be translated into varying degrees of distortion, which shows a significant influence on the structural stability and average voltages. The average voltages obtained here are in good agreement with the experimental values. Furthermore, the possibility of extracting more than one lithium ions per formula unit from Li(2)FeSiO(4) of P2(1)/n is also discussed.

Strain-tunable band gap of hydrogenated bilayer graphene

National Natural Science Foundation of China [10702056, 10774124]; Xiamen University; Academic Award for Doctoral Candidates of China

Ab initio study on the lithiation mechanism of Mg 2 Si electrode

The lithiation mechanism of Mg 2 Si electrode has been investigated using the first-principles calculations within the density functional theory. The detailed reaction paths of lithium insertion into Mg 2 Si were analyzed, and the calculated results indicate that Li 1 Mg 2 Si is just the critical phase, which the substitution of Li and extrusion of Mg begin to happen. The relative volume changes for the electrode were also discussed along with the reaction paths. It is found that the host material first expands then shrinks largely during the whole process of lithium insertion into electrode, it could be one of the important reasons that the pure Mg 2 Si deliver a large initial capacity, but the capacity decreases rapidly with cycling.