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

Abstract

The deployment of Li7La3Zr2O12 (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 Li2CO3/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 Li2CO3/LiOH contamination, it also leads to the formation of the La2Zr2O7 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.