Atomistic Observation of the Lithiation and Delithiation Behaviors of Silicon Nanowires Using Reactive Molecular Dynamics Simulations

For the practical use of silicon nanowires (Si NWs) as anodes for Li-ion batteries, understanding their lithiation and delithiation mechanisms at the atomic level is of critical importance. Here, we report the mechanisms for the lithiation and delithiation of Si NWs determined using a large-scale molecular dynamics (MD) simulation with a reactive force field (ReaxFF). The ReaxFF is developed in this work using first-principles calculations. Our ReaxFF-MD simulation shows that an anisotropic volume expansion behavior of Si NWs during lithiation is dependent on the surface structures of the Si NWs; however, the volumes of the fully lithiated Si NWs are almost identical irrespective of the surface structures. During the lithiation process, Li atoms penetrate into the lattices of the crystalline Si (c-Si) NWs preferentially along the ⟨110⟩ or ⟨112⟩ direction, and then the c-Si changes into amorphous LixSi (a-LixSi) phases due to the simultaneous breaking of Si–Si bonds as a result of the tensile stresses betw...