基于第一性原理Sn-Li合金嵌锂性能和弹性性能的计算与预测

Calculation and prediction of lithium insertion properties and elastic properties for Sn-Li alloy based on first-principle

采用基于密度泛函理论的第一性原理平面波赝势方法,计算锂离子电池负极材料金属Sn在嵌Li过程中形成Li_xSn合金(0≤x≤4.4)的形成能、嵌Li电位、晶体结构、电子结构和弹性性质。结果表明:随着嵌Li量的增加,Li_xSn合金的平均嵌Li电位逐渐降低,体积膨胀率呈现线性增大,费米能态密度整体上呈现增大的趋势,导电性增强。随着嵌Li量的增加,Li_xSn合金中Sn—Li金属键的离子性特征逐渐增强,导致体积模量(B)、剪切模量(G)和弹性模量(E)几乎呈线性降低。G/B值表明,随着嵌Li量的增加,Li_xSn合金由延性转变为脆性,导致LixSn合金容易发生脆性破坏。同时,采用电池程控测试仪测得金属Sn的充放电曲线,发现理论计算的嵌Li电位与实验测得充放电电压具有良好的一致性。

The lithium insertion properties, including formation energy, average intercalation voltage, crystal structure, electronic structure and elastic properties of Li_xSn phase, for pure tin anode material for lithium ion battery 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 average lithium intercalation potential of Li_xSn alloy decreases gradually with Li concentration increasing, the volume expansion rate increases linearly and the density of states at the Fermi level increases, indicating the improvement of electrical conductivity of Li_xSn phase. The ionic nature of Sn—Li metallic band for Li_xSn alloy enhances with Li concentration increasing, resulting in declining of bulk modulus(G), shear modulus(B) and elastic modulus(E). The G/B value shows that mechanical property of Li_xSn alloy changes from toughness to brittleness in high lithium concentration, suggesting that Li_xSn alloy suffer from brittle fracture. On the other hand, the charging-discharging curves of pure tin were measured by battery test instrument. The values of calculated Li intercalated potential obtained DFT calculations are well consistent with the experimental values.