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

The deployment ofLi(7)La(3)Zr(2)O(12) (LLZO) garnetsas solid-state electrolytesfor Li-metalsolid-state batteries faces challenges due to their reactivity withwater and carbon dioxide, resulting in the formation of a Li2CO3/LiOH contamination layer on the LLZO surface. Thiscontamination 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 degrees C) as a thermal cleaning method for LLZO. Byconducting a comprehensive analysis of the LLZO surface using X-rayphotoelectron spectroscopy, hard X-ray photoelectron spectroscopy, in situ grazing incidence synchrotron X-ray diffraction,and Raman spectroscopy, an inherent issue related to high-temperaturethermal cleaning is identified. While heat-treatment effectively reducesthe Li2CO3/LiOH contamination, it also leadsto the formation of the La2Zr2O7 phaseon the LLZO surface due to Li losses. The impact of these factorson the voltage polarization, interfacial resistance, and criticalcurrent density of Li/LLZO/Li symmetrical cells was assessed by electrochemicalimpedance spectroscopy and galvanostatic cycling measurements.