Estimation of the concentration and mobility of mobile Li+ in the cubic garnet-type Li7La3Zr2O12

Abstract

Li₇La₃Zr₂O₁₂ (LLZ) lithium ion conductors with the garnet-like structure are promising candidates for applications in all solid-state lithium ion batteries. Due to the complexity of the structure and the distribution of Li⁺, it was difficult to get information on the true concentration of mobile Li⁺, n_c, and their mobility. In this report, we estimate for the first time the values of n_c from the analysis of the conductivity spectra at different temperatures. We found that only a small fraction of Li⁺ contributes to the conduction process. n_c is found to be independent of temperature with an average value of 3.17 × 10²¹ cm⁻³, which represents 12.3% only of the total Li⁺ content in LLZ garnets. Comparing the conduction parameters of LLZ with Li₆BaLa₂Ta₂O₁₂ (LBLT) and Li₅La₃Ta₂O₁₂ (LLT) garnets indicates that the mobility of Li⁺ plays a prominent role in the conductivity enhancement in LLZ garnet materials. The diffusion coefficient of LLZ at room temperature has a value of 1.33 × 10⁻⁸ cm² s⁻¹, which is comparable with other fast Li⁺ conductors.