Electrochemical stability of garnet-type Li₇La_2.75Ca_0.25Zr_1.75Nb_0.25O₁₂ with and without atomic layer deposited-Al₂O₃ under CO₂ and humidity

Interest toward developing all-solid-state batteries incorporating lithium-stuffed garnet electrolytes (LSGEs) has been on the constant rise. However, LSGEs are known to react with humidity, and subsequently, CO₂ during preparation or storage, leading to Li₂CO₃ formation. In this study, we report the long-term exposure effects of CO₂ and humidity on the lithium-ion conductivity of typical garnet-type Li₇La_2.75Ca_0.25Zr_1.75Nb_0.25O₁₂ with and without Al₂O₃ deposited by atomic layer deposition (ALD). The ionic conductivity of the samples was investigated by electrochemical impedance spectroscopy as a function of time for up to 1000 h. The impedance spectra of ALD-coated garnet-type Li₇La_2.75Ca_0.25Zr_1.75Nb_0.25O₁₂ sample was unaffected by long-term exposure to 400 ppm up to pure CO₂ while the uncoated garnet-type sample show at least 8% increase in total resistance. Both samples show increased resistance in the presence of humidity, but the resistance recovers upon removal of the humidity.