Comparison of alpha- and beta- tin for lithium, sodium, and magnesium storage: an ab initio study including phonon contributions

TL;DR

This study uses ab initio calculations to compare alpha and beta tin phases for lithium, sodium, and magnesium storage, revealing how doping and temperature influence phase stability, intercalation energies, and diffusion barriers relevant to battery applications.

Contribution

It provides a detailed ab initio analysis including phononic effects of phase stability and ion intercalation in tin, highlighting the impact of doping and temperature on phase preferences.

Findings

Mg stabilizes beta-Sn at low concentrations.

Li/Na doping favors alpha-Sn stability up to ~400 K.

Intercalation energies vary significantly with phase and temperature.

Abstract

We present a comparative ab initio study of Li, Na, and Mg storage in tin, including phononic effects and phase competition between alpha and beta Sn. Mg doping at low concentration is found to stabilize the beta phase. On the contrary, Li and Na doping is shown to reverse the stability of the phases at room temperature: Li/Na-doped alpha-Sn is more stable than Li/Na-doped beta-Sn up to a temperature of around 380/400 K. This may rationalize the formation of alpha-Sn upon lithiation and delithiation of beta-Sn anodes reported in experimental studies. The changes in phase stability with Li/Na/Mg doping are directly related to the intercalation energies of Li/Na/Mg in one phase versus the other: at 300 K, Li/Na is easier intercalated in alpha-Sn (-0.37/-0.08 eV) than in beta-Sn (0.06/0.49 eV), while Mg intercalation energy is, although positive (i.e. unfavored intercalation), lower in beta-Sn (0.53 eV) than in alpha-Sn (0.66 eV). The temperature effect is found to affect significantly the intercalation energy, by up to 0.13 eV at 300 K. Analysis of diffusion barriers shows that Li, Na, and Mg diffusion in beta-Sn is anisotropic with migration barriers along the (001) direction (respectively 0.01, 0.22, and 0.07 eV) significantly lower than those in alpha-Sn (respectively 0.20, 0.52, and 0.40 eV).