Concerted influence of microstructure and adsorbed water on lithium-ion conduction of Li1.3Al0.3Ti1.7(PO4)3

Lithium-ion conductors with a crystal structure classified as Na super ion Conductors (NASICON) exhibit high ionic conductivity at room temperature that may be used in next-generation batteries. This study finds unusual ionic conduction of Li1.3Al0.3Ti1.7(PO4)3 (LATP): hysteresis on temperature and atmosphere dependence. The precise conductivity analyses (a wide frequency range, a wide temperature range, and a narrow temperature interval) reveal that the unusual conductivity is attributed to grain boundary conductivity enhanced by moisture. From the detailed studies on bulk (crystal structure) and grain boundary (microcracks, segregation, and impurities) of LATP pellets, it is concluded that the unusual ionic conduction results from adsorbed water on microcracks of LATP pellets. It is also confirmed that at high humidity, grain boundary resistance is further reduced by condensed water in the microcracks. This study reveals the high moisture sensitivity of conductivity of LATP for the first time, which is explained by the concerted influence of microstructure and humidity on ionic conductivity across grain boundaries. The results point out the importance of atmosphere control in scientific studies and for quality control of this class of solid electrolytes in advanced batteries like all-solid-state batteries, Li-air batteries, and others.