Effects of defect on the storage and diffusion of Na and Mg interstitials in Si anode

Abstract

The effects of 90° partial dislocation on the performance of Si anode in Na-ion batteries (NIBs) and Mg-ion batteries (MIBs) are studied by the multi-scale simulation method. In defect-free Si crystal, Na and Mg interstitials prefer to stay at tetrahedral (Td) site and the migration path is Td-Hex-Td. Because of the insufficient binding strength of Na (−0.79 eV) and Mg (−0.969 eV), perfect Si crystal is not suitable for the storage of them. In the presence of 90° partial dislocation, its spacious cores may promote the binding energies of Na and Mg to 0.423 eV and 0.4 eV, respectively. This leads to the insertion of Na and Mg into Si anode possible. Moreover, it is thermodynamically and kinetically favorable for Na and Mg diffusion into the 90° partial dislocation core and surrounding areas. They may concentrate in the dislocation core. This core can also provide a fast diffusion avenue for Na (Mg) by lowing the migration barriers from 1.04 eV (1.02 eV) to 0.75 eV (0.804 eV). Therefore, 90° partial dislocation may improve the charge/discharge rate of NIBs and MIBs.