Si-Li合金相嵌锂性能和弹性性能的第一性原理计算
Calculation of lithium insertion properties and elastic properties for Si-Li alloy phase based on first-principle calculation

采用基于密度泛函理论的第一性原理平面波赝势方法，计算了锂离子电池硅负极材料在嵌Li过程中形成LixSi合金相(0≤x≤4.4)的形成能、嵌Li电位、晶体结构、电子结构和弹性性能。计算结果表明，随着嵌Li量的增加，LixSi合金体系总量能逐渐降低，LixSi合金相的形成能均为负值，表明硅负极材料的嵌Li反应在热力学可以自发进行；随着嵌Li量的增加，LixSi合金相的平均嵌Li电位逐渐降低，体积膨胀率逐渐增大，这与实验测得的结果具有良好的一致性。LixSi合金相在费米能级附近的电子主要由Si原子的p电子和Li原子的s电子共同贡献，LixSi合金相的费米能态密度随着嵌Li量的增加在整体上呈现增大趋势，电子导电性增强。随着嵌Li量的增加，LixSi合金相的体积模量(B)、剪切模量(G)和杨氏模量(E)逐渐降低，G/B值表明LixSi合金相均呈脆性，导致硅在嵌Li过程容易发生脆性结构破坏。
The lithium insertion properties for silicon anode material in lithium ion battery, including formation energies, average intercalation voltages, crystal structures, electronic structures and elastic properties of LixSi alloy phases, were investigated by means of the first-principles plane-wave pseudopotentials method based on the density functional theory (DFT). The calculation results show that the total energy of LixSi alloys gradually reduces with increasing Li concentration and the formation energy is negative, indicating that reaction of Li embedded into silicon is spontaneous in thermodynamics. The average lithium intercalation potential of LixSi alloy phases decreases gradually and the volume expansion rate increases linearly with increasing Li concentration, these phenomena are well consistent with the experimental values. The electrons near the Fermi level of LixSi alloy phases are contributed mainly by p electrons of Si and s electrons of Li. The density of states at the Fermi level increases as a whole with increasing Li concentration, indicating the improvement of electrical conductivity of LixSi alloy phases. The bulk modulus (G), shear modulus (B) and Young’s modulus (E) decline with increasing Li concentration and The G/B value shows that the mechanical properties of LixSi alloys are brittleness, suggesting that LixSi alloys suffer from brittle fracture in process of Li embedded into silicon.