Pyrochlore nanocrystals as versatile quasi-single-source precursors to lithium conducting garnets

Abstract

Lithium conducting garnets are attractive solid electrolytes for solid-state lithium batteries but are difficult to process, generally requiring high reaction and sintering temperatures with long durations. In this work, we demonstrate a synthetic route to obtain Ta-doped garnet (Li6.4La3Zr1.4Ta0.6O12) utilizing La- and Ta-doped lanthanum zirconate (La2.4Zr1.12Ta0.48O7.04) pyrochlore nanocrystals as quasi-single-source precursors.Viamolten salt synthesis (MSS) in a highly basic flux, the pyrochlore nanocrystals transform to Li-garnet at reaction temperatures as low as 400 °C. We also show that the pyrochlore-to-garnet conversion can take place in one step using reactive sintering, resulting in densified garnet ceramics with high ionic conductivity (0.53 mS cm−1at 21 °C) and relative density (up to 94.7%). This approach opens new avenues for lower temperature synthesis of lithium garnets using a quasi-single-source precursor and provides an alternative route to highly dense garnet solid electrolytes without requiring advanced sintering processes.