Medium-temperature solid-state batteries based on sodium-beta alumina

The demand for more powerful and cost-effective electrochemical energy storage systems is increasing. One focus is research into so-called "post-Li-ion" batteries, which are not based on lithium but on other alkali or alkaline earth metals, such as potassium or calcium. Another prominent approach is using sodium, e.g., as a negative electrode (hereafter: anode), in combination with a solid electrolyte, resulting in solid-state sodium cells. The ceramic, polycrystalline sodium-beta alumina solid electrolyte (BASE) might be a viable candidate due to its outstanding electrochemical properties, low cost, and abundant raw materials. As positive electrodes, intercalation-type positive electrodes might be viable. These are already used successfully in Li-ion systems. Notwithstanding, there is barely any research about combining these material combinations to a cell systems operating below 100 °C yet (δm, Na = 97.7 °C). This thesis gives attention to this fact. The project focuses on clarifying the requirements for and the construction of cells consisting of metallic sodium anodes, sodium-beta alumina, and Na-ion cathodes, which are operated at temperatures below 100 °C. The work highlights the challenges for this specific material combination, suggests possible compositions and instructions for action. It provides initial characteristic values for the system. In doing so all three core components of the cell, i.e., the anode, the cathode, and the solid electrolyte, and their interaction are considered. As the solid electrolyte is the core component of the cell system, three publications (Publication 1, Publication 2, Publication 3) are dedicated to this essential cell component. The interaction of anode and solid electrolyte is examined in Publications 2 and 4. Publications 4 and 5 show the combination of Na-ion cathodes with the solid electrolyte and investigate the resulting cell system.