Cubic phases of garnet-type Li7La3Zr2O12: the role of hydration

Abstract

We address the controversial issue of the structural stability of Li 7 La 3 Zr 2 O 12 garnets, focusing on the mechanisms that result in the transformation from tetragonal to cubic symmetry. We show that undoped tetragonal Li 7 La 3 Zr 2 O 12 not exposed to humidity at any moment undergoes a reversible phase transition to cubic symmetry at T c x 645 C that we ascribe to lithium dynamic effects. On the other hand, a close correlation has been found between the appearance of a cubic phase between 100 and 200 C in X-ray diffractograms and the presence of water, either in the atmosphere in which experiments are performed or already in the starting material. The natures of the high and lowtemperature cubic garnets are totally different: the one found above the phase transition does not involve any change in the stoichiometry, whereas the cubic phase formed at low temperature is a hydrated, lithium defective phase, due to the combined effect of water insertion into the garnet structure and the H + /Li + exchange mechanism. Differences in the actual compositions of the samples depending on their thermal history are corroborated by TG-MS experiments. Chemical reactions and phases formed along the thermal evolution are elucidated with the help of Raman spectroscopy.

Reversible ion exchange and structural stability of garnet-type Nb-doped Li7La3Zr2O12 in water for applications in lithium batteries

“…5. A large weight loss of 5.7% in the temperature range of 200e600 C can be discovered, accompanied with an endothermic peak at 396 C in the DSC curve, which was close to the reported value of hydrated LLZ samples [29]. The weight loss was mainly ascribed to the release of H 2 O and agreed with the amount of 5.6% calculated from the ICP results.…”

Electrochemical Stability of Li6.5La3Zr1.5M0.5O12 (M = Nb or Ta) against Metallic Lithium

“…In addition, the Raman spectra were consistent with the spectra of cubic LLZTO reported by Thompson et al (2014). The LLZTO band at ~640 and ~740 cm −1 are related with Zr-O bond stretching (Tietz et al, 2013;Larraz et al, 2013) and Ta-O bond stretching (Thompson et al, 2014), respectively. Therefore, the LLZNO band at ~640 and ~720 cm −1 of LLZNO can be assigned to the stretching of ZrO6 and NbO6 octahedron, respectively.…”

Hybrid Polymer/Garnet Electrolyte with a Small Interfacial Resistance for Lithium‐Ion Batteries

“…The reduction of the Raman peak width and the symmetry change of LLZT may be related to the Li loss. [11] Typical signals of CO 3 2À are observed in fixed spots of the mapping spectra in Figure 2 c,d, 400 different positions (spot size 3 3 mm 2 ) in one 50 50 mm 2 area were selected for the Raman mapping. The color in Figure 2 c and d corresponds to the integral area, which was calculated from the characteristic peak of Li 2 CO 3 at 1090 cm À1 .…”