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

Crystalline lithium silicides LixSiy 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.