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.

Key words: Mechanical properties; Thermal conductivity; Lithium-ion batteries; Elastic anisotropy; First-principles calculations

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