Instability of the Lithium Garnet Li₇La₃Sn₂O₁₂: Li⁺/H⁺ Exchange and Structural Study

Abstract

We demonstrate for the first time the instability of the lithium garnet Li 7 La 3 Sn 2 O 12 toward moisture. In ambient air a spontaneous Li þ /H þ exchange occurs leading to Li 7-x H x La 3 Sn 2 O 12 . The lithium released is combined with the atmospheric CO 2 under the Li 2 CO 3 form making Li 7 La 3 Sn 2 O 12 a CO 2 absorbent. The structural study of the exchanged Li 7-x H x La 3 Sn 2 O 12 phase has been performed on samples obtained by heating at reflux the mother compound in a solution of benzoic acid/ ethanol during one week. After chemical analysis of the lithium content and thermal analysis, the compound has been structurally characterized by the Rietveld method from powder and single crystal XRD experiments. It was found to crystallize in the cubic space group Ia3d with a Li þ distribution comparable to that observed in other cubic lithium garnets: three lithium sites partially occupied (24d, 48g, and 96h). The total ionic conduction of the exchanged garnet has been studied by impedance spectroscopy and compared to that of the mother form Li 7 La 3 Sn 2 O 12 . This study revealed that after Li þ /H þ exchange the conduction remains unchanged.

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

“…It was demonstrated that the instability of Li 7 La 3 Zr 2 O 12 (Al) in water led to the decrease of ionic conductivity of ceramic bulk samples [18]. The spontaneous ionexchange phenomenon in the ambient air was also observed in tetragonal Li 7 La 3 Sn 2 O 12 [19]. Similar proton ion-exchange phenomena also occurred in other solid electrolytes such as Li 0.30 La 0.57 TiO 3 with perovskite structure [20].…”

Structural limitations for optimizing garnet-type solid electrolytes: a perspective

“…27 One, however, needs to be very careful in the selection of elements, since a substitution on the octahedral Li-site will result in a blocking of the diffusion pathways. Nevertheless, considering the known structural instability of these compounds to humidity and air, which lowers the ionic conductivity significantly, [74][75][76] it seems difficult to obtain the necessary ionic conductivity using the current approaches. However, there is a wide variety of promising materials systems such as glassy materials, glass ceramics, Li rich anti-perovskites and sulfide superionic conductors (e.g.…”

Aqueous Lithium-Air Batteries

“…However, the impedance profiles did reveal a change after immersion in these solutions, as shown in Fig. 4 [39]. An increase of grain boundary resistance was also observed for Li 1 3 , which has high lithium-ion conductivity and is stable in saturated LiOH with saturated LiCl, is thus a promising candidate for the protective layer of a water-stable lithium electrode.…”