In Situ Neutron Diffraction Monitoring of Li₇La₃Zr₂O₁₂ Formation: Toward a Rational Synthesis of Garnet Solid Electrolytes.

Abstract

The favorable combination of fast-ionic conductivity and high electrochemical stability of Li-stuffed garnet type Li 7 La 3 Zr 2 O 12 (LLZ) makes this material a promising candidate for applications as a solid-state electrolyte in high-energy-density batteries. However, a widespread technical use of LLZ is impeded by difficulty in reliable formation and densification of the pure fast-ion conducting phase. The present study of the phase-formation process enables rational fabrication procedures to be devised based on a thorough understanding of the complex phase formation of LLZ. In situ neutron powder diffraction monitoring of the phase formation revealed an influence of the partial melting of precursors on the formation of the fast-ion conducting phase, indicating that in the typical synthesis route LLZ is not formed in a solid-state reaction but from a partial carbonate melt that decomposes on further heating. The cooling rate critically influences lithium ordering and ionic conductivity.

A study of suppressed formation of low-conductivity phases in doped Li7La3Zr2O12 garnets by in situ neutron diffraction

“…The Reaction (2) and Reaction (3) are thus considered as a part of the reaction for LLZO but not the side reactions. The formation of garnet accompanies the melting of Li 2 CO 3 (agreeing with the literature37 ), which starts to melt at ~ 730 °C. During the dwell at 800 °C before Reaction (4) completes, crystalline Li 2 CO 3 disappears because it is in the form of liquid and does not produce Bragg peaks.…”

“…The formation of La 2 Zr 2 O 7 that has strong appearance in neutron diffraction was observed in Ta and Nb doped LLZO. 37 Subsequently, the formation of garnets starts around 710~720 °C by the reaction 2La 2 O 3 + 5Li 2 CO 3 + 2Li 2 ZrO 3 + La 2 Zr 2 O 7 → 2Li 7 La 3 Zr 2 O 12 + 5CO 2 (4) and the synthesis finishes after the 800 °C dwell. …”

Effect of Li+/H+ exchange in water treated Ta-doped Li7La3Zr2O12

“…(4), La 2 O 2 CO 3 , has also been identified in our recent neutron in situ study [24] as an intermediate species in the formation of LLZ. The decomposition of lanthanum hydroxycarbonate hence appears as a plausible source of CO 2 for the sintered pellet despite the absence of Li 2 CO 3 peaks from XRD and hardly any weight loss in the temperature range where Li 2 CO 3 would decompose.…”

High lithium ionic conductivity in the garnet‐type oxide Li7−2xLa3Zr2−xMoxO12 (x=0‐0.3) ceramics by sol‐gel method

“…This stabilization effect of Mo is similar with those of Te and W substituting. On the other hand, little La 2 O 3 impurity has been detected as the secondary phase for composition with x =0 (~3.3 wt%) and 0.1 (~1.2 wt%), which is consistent with the recent neutron diffraction results . When the addition of Mo is higher than 0.1, La 2 O 3 secondary phase has disappeared.…”