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Garnet-type solid electrolytes are one of key materials to enable practical usage of lithium metal anode for high-energy-density batteries. However, it suffers from lithium growth in pellets on charging, which causes short circuit. In this study, grain boundaries of Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZT) pellets are modified with Li 2 CO 3 and LiOH to investigate the influence of the microstructure of grain boundaries on lithium growth and to study the mechanism of the lithium growth. In spite of similar properties (relative density of ca. 96% and total ionic conductivity of 7 × 10 −4 S cm −1 at 25 °C), the obtained pellets exhibit different tolerance on the short circuit. The LLZT pellets prepared from LiOH-modified LLZT powders exhibit rather high critical current density of 0.6 mA cm −2 , at which short circuit occurs. On the other hand, the LLZT pellets without grain boundary modification short-circuited at 0.15 mA cm −2 . Microstructural analyses by means of SEM, STEM and EIS suggest that lithium grows through interconnected open voids, and reveal that surface layers such as Li 2 CO 3 and LiOH are not only plug voids but also facilitate the sintering of LLZT to suppress the lithium growth. The results indicate a strategy towards short-circuit-free lithium metal batteries. [ABSTRACT FROM AUTHOR]

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 Li 1.3 Al 0.3 Ti 1.7 (PO 4) 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. [Display omitted] • NASICON-type lithium ion conductor LATP exhibits atmosphere-dependent conductivity. • Adsorbed water causes lattice shrinkage. • Grain boundary resistance decreases by adsorbed and condensed water on microcracks. • LiPO 3 impurity causes irreversible humidity-dependent conductivity. [ABSTRACT FROM AUTHOR]