Stability of low-temperature Li7La3Zr2O12 cubic phase: The role of temperature and atmosphere

Rechargeable all solid-state lithium batteries are a promising technology for the next generation of safer batteries. In this context, strict requirements are placed on the electrolytes, among which is emerging the Li7La3Zr2O12 garnet, chiefly for the relationships among synthesis conditions and phase stability. Here, the structural modifications of the low temperature (LT) Li7La3Zr2O12 cubic form were investigated by using in situ X-Rays diffraction analysis. In particular, we studied the role of both temperature and atmosphere (air or argon) on phase stabilization. In argon flow, the LT phase is stable under 750 C, and it transforms into the tetragonal one at lower temperature. In air, it partially decomposes to La2Zr2O7 due to Li loss above 250 C. ICP-OES analysis confirmed that garnet stoichiometry was maintained in argon, whereas in air lithium loss occurred. The structural transformations are driven by the CO2 absorbed in the LT structure that can form Li2CO3 and/or La2(CO3)3 so causing stoichiometry changes responsible of the structural evolution