Reaction mechanisms of lithium garnet pellets in ambient air: The effect of humidity and CO2.

Li7La3Zr2O12 ( LLZO) has been reported to react in humid air to form Li2 CO3 on the surface, which decreases ionic conductivity. To study the reaction mechanism, 0.5-mol Ta-doped LLZO (0.5Ta- LLZO) pellets are exposed in dry (humidity ~5%) and humid air (humidity ~80%) for 6 weeks, respectively. After exposure in humid air, the formation of Li2 CO3 on the pellet surface is confirmed experimentally and the room-temperature ionic conductivity is found to drop from 6.45×10−4 S cm−1 to 3.61×10−4 S cm−1. Whereas for the 0.5Ta- LLZO samples exposed in dry air, the amount of formed Li2 CO3 is much less and the ionic conductivity barely decreases. To further clarify the reaction mechanism of 0.5Ta- LLZO pellets with moisture, we decouple the reactions between 0.5Ta- LLZO with water and CO2 by immersing 0.5Ta- LLZO pellets in deionized water for 1 week and then exposing them to ambient air for another week. After immersion in deionized water, Li+/H+ exchange occurs and Li OH H2O forms on the surface, which is a necessary intermediate step for the Li2 CO3 formation. Based on these observations, a reaction model is proposed and discussed. [ABSTRACT FROM AUTHOR]