Thermal expansion in the garnet-type solid electrolyte (Li_7−xAl_x/3)La₃Zr₂O₁₂ as a function of Al content

Highlights: • Thermal expansion (TE) coefficients of LLZ found up to 700°. • The aluminum content of LLZ has a small impact on the thermal expansion. • Typical thermal expansion values were around, 16 × 10⁻⁶ K⁻¹. • The TE is approximately double other garnet-type structures. - Abstract: The thermal expansion (TE) coefficients of the lithium-stable lithium-ion conducting garnet lithium lanthanum zirconium oxide (LLZ) and the effect of aluminum substitution were measured from room temperature up to 700 °C by a synchrotron-based X-ray diffraction. The typical TE value measured for the most reported composition (LLZ doped with 0.3 wt.% or 0.093 mol% aluminum) was 15.498 × 10⁻⁶ K⁻¹, which is approximately twice the value reported for other garnet-type structures. As the Al(III) concentration has been observed to strongly affect the structure observed and the ionic conductivity, we also assessed its role on thermal expansion and noted only a small variation with increasing dopant concentration. The materials implications for using LLZ in a solid state battery are discussed