Thermal expansion in the garnet-type solid electrolyte (Li7−xAlx/3)La3Zr2O12 as a function of Al content

•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, 16×10−6K−1.•The TE is approximately double other garnet-type structures. 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 0.3wt.% or 0.093mol% aluminum) was 15.498×10−6K−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.