12:15 〜 12:30
▲ [21a-S322-13] Alpha-Sn versus Beta-Sn Anodes for Li-, Na-, and Mg-ion Batteries: a First-Principles Study Including the Effect of Phonons
キーワード：lithium ion battery,sodium ion battery,tin anode
Tin is extensively researched as anode material for Li, Na, and Mg ion batteries. Initial stages of charge proceed via solid solution and affect relative phase stability of alpha vs beta Sn. We present a comparative ab initio study of Li, Na, and Mg insertion in alpha and beta Sn, including phononic effects. 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 (to compare to alpha-beta transition temperature of ~290 K in pure Sn). 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, with negative values for thermodynamically favored insertion vs Li/Na bulk formation) 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 vs bulk Mg) 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).