A Comparative Computational Study of Structures, Diffusion, and Dopant Interactions between Li and Na Insertion into Si

We present a comparative computational study of sodiated vs lithiated bulk Si, including the effects of Li-Li and Na-Na interactions on dopant mobility. Both Na and Li prefer to act as interstitial defects located at the tetragonal sites of the Si matrix. The migration barrier between tetragonal sites is 0.54 eV larger for Na than for Li, which is expected to result in a drastically lower diffusion rate. The interdopant interactions reduce the barrier for Li and Na diffusion by 0.16 and 0.28 eV, respectively, providing ab initio evidence that finite ion concentrations may improve the battery charge/discharge rate. (C) 2013 The Japan Society of Applied Physics