Li$^+$ diffusion in crystalline lithium silicides: influence of intrinsic point defects

Abstract Crystalline lithium silicides Li$_x$Si$_y$ are a group of Zintl-like compounds, of which Li$_{15}$Si$_4$ is observed crystallizing in Si anodes after complete electrochemical lithiation. Here, Li diffusion in Li$_1$Si$_1$, Li$_{12}$Si$_7$, Li$_{13}$Si$_4$ and Li$_{15}$Si$_4$ is extensively studied by means of ab initio molecular dynamics simulations and nudged elastic band calculations considering various intrinsic point defects. Li interstitials are identified as the main vehicle of diffusion due to typically low formation and migration energies. They diffuse via an interstitialcy mechanism usually involving 2 or 3 atoms. Moreover, Frenkel defects are found to play a role in Li$_{12}$Si$_7$ and Li$_{13}$Si$_4$ only, as their formation energies are relatively high in Li$_1$Si$_1$ and Li$_{15}$Si$_4$. All investigated intrinsic defects have an impact on energy barriers of nearby as well as farther diffusion paths.