Effects of Gallium Doping in Garnet-Type Li₇La₃Zr₂O₁₂ Solid Electrolytes

Garnet-type Li₇La₃Zr₂O₁₂ (LLZrO) is a candidate solid electrolyte material that is now being intensively optimized for application in commercially competitive solid state Li⁺ ion batteries. In this study we investigate, by force-field-based simulations, the effects of Ga³⁺ doping in LLZrO. We confirm the stabilizing effect of Ga³⁺ on the cubic phase. We also determine that Ga³⁺ addition does not lead to any appreciable structural distortion. Li site connectivity is not significantly deteriorated by the Ga³⁺ addition (>90% connectivity retained up to <i>x</i> = 0.30 in Li_{7–3<i>x</i>}Ga_<i>x</i>La₃Zr₂O₁₂). Interestingly, two compositional regions are predicted for bulk Li⁺ ion conductivity in the cubic phase: (i) a decreasing trend for 0 ≤ <i>x</i> ≤ 0.10 and (ii) a relatively flat trend for 0.10 < <i>x</i> ≤ 0.30. This conductivity behavior is explained by combining analyses using percolation theory, van Hove space time correlation, the radial distribution function, and trajectory density