On High-Temperature Thermal Cleaning of Li₇La₃Zr₂O₁₂ Solid-State Electrolytes

High Resolution Image Download MS PowerPoint Slide The deployment of Li 7 La 3 Zr 2 O 12 (LLZO) garnets as solid-state electrolytes for Li-metal solid-state batteries faces challenges due to their reactivity with water and carbon dioxide, resulting in the formation of a Li 2 CO 3 /LiOH contamination layer on the LLZO surface. This contamination layer contributes to high Li/LLZO interfacial resistance, voltage polarization at the Li anode, and the formation of Li dendrites. In this work, we study the feasibility of high temperature annealing (600–900 °C) as a thermal cleaning method for LLZO. By conducting a comprehensive analysis of the LLZO surface using X-ray photoelectron spectroscopy, hard X-ray photoelectron spectroscopy, in situ grazing incidence synchrotron X-ray diffraction, and Raman spectroscopy, an inherent issue related to high-temperature thermal cleaning is identified. While heat-treatment effectively reduces the Li 2 CO 3 /LiOH contamination, it also leads to the formation of the La 2 Zr 2 O 7 phase on the LLZO surface due to Li losses. The impact of these factors on the voltage polarization, interfacial resistance, and critical current density of Li/LLZO/Li symmetrical cells was assessed by electrochemical impedance spectroscopy and galvanostatic cycling measurements.