锂离子电池硅基负极材料嵌锂行为的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势方法,计算不同数量的锂离子引起的硅材料晶体结构的变化以及在嵌锂过程中形成Li_xSi(x=1、2、2.4、4.4)合金相的形成能与电子结构.采用LST/QST方法计算过渡态,模拟合金体相中的锂离子迁移过程.计算结果表明,随着嵌锂数量的增加,硅晶胞的体积在不断增大;Li_xSi合金相的形成能为负值,表明在嵌锂过程中锂离子和硅原子可以自发形成这些合金相,其中Li₇Si₃合金最容易形成;随着嵌锂量的增加,锂离子在费米能级处s轨道提供的电子数逐渐增加,锂硅合金在费米能级处的电子数量呈增大趋势,表明锂硅合金的导电性越来越优;常温下Li₂Si体相中很难直接形成锂离子空位,但锂离子空位的迁移过程很容易发生.

First-principles study on lithium insertion behavior of silicon-based anode materials for lithium ion batteries

The-first-principle plane wave pseudopotential method based on density functional theory is used to calculate the crystal structure changes of silicon materials caused by different amount of lithium ions and the formation energies and electronic structures of LixSi (x=1, 2, 2.4, 4.4) alloy phase formed in the lithium intercalation process. The transition states were calculated by LST/QST method to simulate the lithium ion migration process in the alloy bulk. The results show that the volume of the silicon cells increases with the increase of the amounts of lithium intercalation, and the formation energies of LixSi alloy phase are negative, which indicates that these alloy phases can be spontaneously formed by lithium ion and silicon atom in the process of lithium intercalation, among which Li7Si3 alloy is the easiest to form. With the increase of lithium intercalation, the number of electrons provided by s orbit at Fermi level of lithium ion gradually increases, and the number of electrons in Fermi level of lithium silicon alloy decreases, which indicate that the conductivity of Li-Si alloy is increasingly excellent. It is difficult to form lithium ion vacancy directly in Li2Si bulk phase at room temperature, but the migration of lithium ion vacancy is easy to occur.