The Effect of Crystallographic Orientation on the Lithiation and Delithiation of Si: A Molecular Dynamics Study

Abstract

Drastic volume change during lithiation and delithiation gives the biggest challenge in the realization of Si anode in commercial Li-ion batteries. Especially, the anisotropic volume expansion has been thought to be the most important feature for electrochemical reactions of Si nanowire anodes, since it could give an inspiration in designing advanced battery anodes. In the present study, initial stage of lithiation and delithiation processes of Si anodes has been investigated using a large scale molecular dynamics simulation based on a recently developed 2NN MEAM interatomic potential for the Li-Si system. A crystal-to-amorphous transition during lithiation process to different directions was simulated and especially, the ledge-mediated mechanism was correctly reproduced. A transition behavior and rate is highly dependent on the crystallographic orientation of Si, which provides a key explanation for the important anisotropic volume expansion in Si wire anodes. And, the lower degree of pulverization in Si wire than Si film during delithiation simulation was observed, in a qualitative agreement with general perception.