All‐solid‐state batteries with an alkali metal anode have the potential to achieve high energy density. However, the onset of dendrite formation limits the maximum plating current density across the solid electrolyte and prevents fast charging. It is shown that the maximum plating current density is related to the interfacial resistance between the solid electrolyte and the metal anode. Due to their high ionic conductivity, low electronic conductivity, and stability against sodium metal, Na‐β″‐alumina ceramics are excellent candidates as electrolytes for room‐temperature all‐solid‐state batteries. Here, it is demonstrated that a heat treatment of Na‐β″‐alumina ceramics in argon atmosphere enables an interfacial resistance <10 Ω cm2 and current densities up to 12 mA cm−2 at room temperature. The current density obtained for Na‐β″‐alumina is ten times higher than that measured on a garnet‐type Li7La3Zr2O12 electrolyte under equivalent conditions. X‐ray photoelectron spectroscopy shows that eliminating hydroxyl groups and carbon contaminations at the interface between Na‐β″‐alumina and sodium metal is key to reach such values. By comparing the temperature‐dependent stripping/plating behavior of Na‐β″‐alumina and Li7La3Zr2O12, the role of the alkali metal in governing interface kinetics is discussed. This study provides new insights into dendrite formation and paves the way for fast‐charging all‐solid‐state batteries.

Hydrogen produced by water electrolysis with renewable electricity is a reliable, affordable and environmental friendly energy carrier for future energy supply and storage. Alkaline water electrolysis is a well matured technique and proved to be suitable for large-scale applications. Materials development for alkaline water electrolyzers is still of interest for academia and industry to address the issues of low compatibility to renewable power sources. A lab-scale system for alkaline water electrolysis was developed, aiming to advance materials development and to bridge the intrinsic properties of materials with their performance under realistic operating conditions. As the smallest pressure-type electrolyzer, it is capable of working at 30 bar and 80 °C with continuous liquid electrolyte circulation. Experimental studies investigate the influence of temperature, pressure, and intrinsic properties of materials on voltage efficiency and hydrogen purity. With appropriate analysis, links between material specifications and overall performance can be established, encouraging new designs and material innovations for alkaline water electrolysis.

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Li 7 La 3 Zr 2 O 12 (LLZO) garnet ceramics are promising electrolytes for all-solid-state lithium-metal batteries with high energy density. However, these electrolytes are prone to Li + /H + exchange, that is, protonation, resulting in degradation of their Li-ion conductivity. Here, we identify how common processing steps, such as surface cleaning in alcohol or acetone, trigger LLZO partial protonation. We deconvolute the contributions to the electrochemical impedance spectra of both the protonated LLZO phase (HLLZO) and its decomposition products forming upon annealing. While the mixed conduction of H + / Li + ions in HLLZO decreases the contribution of the electrolyte to the overall impedance, it deteriorates the transport of Li + ions across the LLZO/Li interface. This is also the case after thermal decomposition of HLLZO, which occurs at significantly lower temperature than that for pristine LLZO. As a result, symmetric Li/LLZO/Li cells suffer from inhomogeneous lithium electrodeposition within the first three cycles when stripping and plating a capacity of 1 mA•h/cm 2 per half-cycle at 0.1 mA/cm 2 . We demonstrate that LLZO protonation is avoided when applying solvents with very low acidity, such as hexane. Such Li/LLZO/Li cells provide stable cycling over more than 300 h, demonstrating the importance of selecting an appropriate solvent for LLZO processing to prevent dendrites formation.

Na-β″-alumina ceramics are archetypical ion conductors with excellent sodium-ion conductivity. Their processing is, however, challenging and results in large variations in reported conductivity measurements. We systematically reexamine the impact of sintering conditions on microstructure and sodium-ion conductivity of Na-β″-alumina ceramics. Depending on sintering temperature and sintering time, we measure conductivities between 0.04 and 0.37 S/cm at 300 °C on ceramics prepared from identical starting powders. During sintering, formation of a liquid phase is observed above 1500 °C, which promotes densification but leads to abnormal grain growth for extended sintering times. While such conditions result in the highest conductivities measured for our sample series (0.37 S/cm at 300 °C), the corresponding microstructures are mechanically fragile. For mechanically robust, densely sintered samples, we identify the average grain size as the dominating factor controlling ion conductivity. For average grain sizes between 1 and 6 μm, we obtain conductivities between 0.17 and 0.27 S/cm at 300 °C. The influence of porosity in undersintered, highly porous samples is well accounted for by Archie’s law and results in low ion conductivities down to 0.04 S/cm at 68% density. Our insights into microstructural factors controlling ionic conductivity such as grain size and density are instrumental for the successful integration of Na-β″-alumina ceramic electrolytes into next-generation batteries.