Li嵌入Mg_2Ge的反应次序和电子结构变化

The reaction sequence of lithiation in Mg_2Ge and the changes of its electronic structure

Mg2Ge有望成为新的锂离子电池负极材料.使用基于平面波展开的第一性原理赝势法,计算并得到了Li嵌入Mg2Ge负极材料时的反应次序.Li首先占据其中的间隙位置,占满间隙位置后随着嵌Li量的进一步增加,Li将逐步替位Mg2Ge中一半的Mg位置,直到生成Li2MgGe.计算结果表明,在整个嵌Li过程中主体材料的体积先膨胀后收缩,体积胀缩量很大,这是导致Mg2Ge作为锂离子电池电极材料循环性能较差的重要原因.对材料电子结构的分析表明,随着Li嵌入量的增加,主体材料发生了从半导体性到金属性、又到半金属性的转化.

Mg2Ge is a promising new anode material for lithium ion batteries.The ab initio pseudopotential method with the plane wave expansion of the crystal wave function was employed to study the lithiation properties of anode material Mg2Ge.The reaction sequence of lithiation in Mg2Ge have been calculated.It was found that Li ions firstly occupy the interstitial sites until the interstitial sites are full,and then substitute the Mg sites until half of the Mg sites are replaced to form the phase of Li2MgGe.The calculation results also show that the crystal volume firstly expands and then shrinks as the number of Li ions increases.The changes of crystal volume are very big during the whole process which is the cause of bad cycle performance of the material.The electronic structures are also analyzed,which indicates that the host material changes from semiconducting to metallic then to semiconducting with the increase of Li intercalations.