First-Principles Investigation of the Mechanical and Thermodynamic Properties of the Metal-Borohydrides as Electrolytes for Solid-State Batteries

Abstract

The structural, elastic, Vickers hardness, anisotropy and thermodynamic properties of M2B10H10 (M = Li, Na and K) are systematically investigated using the pseudopotentials plane waves methods within the general gradient approximation in the framework of density functional theory. The calculated lattice parameters of Li2B10H10 are in excellent agreement with the experimental data. The lattice parameters of hexagonal structure Na2B10H10 and K2B10H10 are predicted. The elastic constants of M2B10H10 reveal that they are mechanically stable. The polycrystalline modulus including the bulk and shear modulus, the Young's modulus, Poisson ratio, B/G, Vickers hardness and Debye temperature are also calculated. According to the obtained results, Li2B10H10 is brittle material, while Na2B10H10 and K2B10H10 are ductile material and all of them can be classifieds as “soft material”. The anisotropy factors demonstrate that M2B10H10 exhibit large anisotropy, and all of them have more elastic anisotropy in compression than in shear. Finally, the Debye temperature, minimum thermal conductivity and melting point of M2B10H10 are also predicted, the results shows that the Li2B10H10 is more suitable for solid electrolyte than Na2B10H10 and K2B10H10.