Mechanical, acoustical, and optical properties of several Li-Si alloys: a first-principles study

Abstract

Owing to their excellent theoretical capacity, Li-Si alloys have been extensively investigated as potential Lithium-ion batteries. Knowledge of the mechanical, acoustical, and optical properties of Li-Si alloys is important in order to improve battery performance. In the present study, we calculated the mechanical, acoustical, and optical properties of several Li-Si alloys theoretically. Our investigation confirms the mechanical stability of these Li-Si alloys. With increasing lithium content, Li-Si alloys become increasingly vulnerable to shape deformation as the number of Si-Si bonds decreases. The analysis of elastic moduli shows that the bulk modulus increases with the increase of lithium contents. Li₂₂Si₅ has the strongest anisotropic Young’s modulus. The sequence of degree of anisotropic Young’s modulus is Li₂₂Si₅>Li₁₅Si₄>LiSi>Li₁₇Si4>Li₁₂Si₇>Li₁₃Si₄. From an analysis of the anisotropy of acoustic velocity, the transverse velocities are shown to be less than the corresponding longitudinal acoustic velocities. The longitudinal wave of the cubic system is the fastest along the [111] direction, while it is the fastest along the [001] direction for the orthorhombic system and the [010] direction for the tetragonal system. In addition, all the studied Li-Si alloys have relatively low thermal conductivities and show a higher anisotropy when photon energies are lower than 20 eV. We conclude that the studied Li-Si alloys are promising dielectric materials.

概 要

锂硅合金作为潜在的锂离子电池已被广泛研究。 了解锂硅合金的力学、声学和光学性质对于改进 电池的性能非常重要。 本文从理论上研究了几种 锂硅合金的一系列特性。研究表明, 这些锂硅合 金具有力学稳定性。 随着锂浓度的增加, 锂硅合 金中 Si-Si 键减少, 从而使其越来越容易变形。 弹性模量的分析表明, 随着锂浓度的增加, 体模 量增加, 且 Li₂₂Si₅ 的杨氏模量各向异性最强。杨 氏模量各向异性强度的次序为: Li₂₂Si₅>Li₁₅Si₄> LiSi>Li₁₇Si₄>Li₁₂Si₇>Li₁₃Si₄。 从声速的各向异性 分析得知, 横向声速小于相应的纵向声速。 立方 体系的纵波在[111]方向最快, 正交体系的纵波在[001]方向最快, 而四方晶系的纵波在[010]方向最 快。 所研究的锂硅合金的导热性较低, 且当光子 能量小于 20 eV 时, 显示出较高的各向异性。