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 Li₁₅Si₄ is observed crystallizing in Si anodes after complete electrochemical lithiation. Here, Li diffusion in Li₁Si₁, Li₁₂Si₇, Li₁₃Si₄ and Li₁₅Si₄ 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 Li₁₂Si₇ and Li₁₃Si₄ only, as their formation energies are relatively high in Li₁Si₁ and Li₁₅Si₄. All investigated intrinsic defects have an impact on energy barriers of nearby as well as farther diffusion paths.