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

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 x 10(21) 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 x 10(-8) cm(2) s(-1), which is comparable with other fast Li+ conductors.