Guidelines to correctly measure the lithium ion conductivity of oxide ceramic electrolytes based on a harmonized testing procedure

Ionic conductivities of Li-ion conducting ceramic electrolytes, mostly evaluated by means of impedance spectroscopy, are a key parameter decisive for their application. Nevertheless, significant deviations in the ionic conductivity of nominally identical samples are reported in literature, which are attributed to material and sample preparation as well as measurement related differences. The goal of this study is a detailed assessment of impedance measurement deviations of 10 identically prepared samples of each Li6.45La3Zr1.6Ta0.4Al0.05O12 (LLZO:Ta:Al) and Li1.3Al0.3Ti1.7(PO4)3 (LATP), respectively. By introducing a harmonized testing procedure for impedance measurement and data analysis, deviations among the participating labs were reduced to differences <1.8% for LLZO and <3.1% for LATP. A complete assessment of instrumentation (fitting, temperature and impedance measurement errors) and sample geometry related errors revealed a high measurement precision with a total error <1.1%. Further on a decreasing ionic conductivity was observed for both materials during the study. Indications for testing and storage induced aging mechanisms were obtained by additional measurements.