Ab Initio Investigation of the Elastic Properties of CaxSn1−x Alloys for Use As Battery Anodes

Abstract

Density functional theory has been used to investigate 19 CaxSn1−x structures (six bulk materials and 13 alloys) as potential battery anodes. Of the alloys, we have found four stable phases (x = 0.25, 0.5, 0.625, and 0.75) and three metastable phases (two at x = 0.5 and one at x = 0.75). For the (meta)stable phases, we compare quantities such as the elastic moduli (bulk (K), shear (G), and Young’s (E)), Poisson’s ratio (ν) and the Pugh ratio (γ), the latter two being metrics for ductility. Nearly all of the alloys exhibit a steady increase in G (from 21.6 GPa to 25.3 GPa) and E (56.1 GPa to 59.1 GPa). K ranges from 25.7 GPa to 46.3 GPa across the same concentration window. For bulk Sn, the ν and γ values are close to the ductile/brittle boundary, followed by an increase in ductility to the peak value at x = 0.25 (ν = 0.298 and γ = 2.14), beyond which both quantities decrease reaching a minimum value at x = 0.75 (ν = 0.168 and γ = 1.17). The Debye temperature (θD) and minimum thermal conductivity (kmin) of each compound were also calculated, following a trend that is identical to the shear modulus. We have found that for stable/metastable compositions of CaxSn1−x, those sharing the same chemical composition (stoichiometry) also share remarkably similar material properties, indicating that such materials would be advantageous for uses in battery anodes.