Sodium-beta-alumina batteries: A review of Na-Al inorganic molten salt battery

The urgent global demand for sustainable and efficient energy storage solutions has intensified research into advanced battery technologies, particularly those suitable for large-scale stationary applications. This review provides a comprehensive examination of sodium-beta-alumina batteries (NBBs) employing molten metallic sodium (Na(l)) as the negative electrode and aluminum-based positive electrodes, with a focus on the Na-Al system. Key components such as the molten electrolyte NaAlCl 4 , the beta-alumina solid electrolyte (BASE), and the interfacial challenges between Na(l) and BASE are critically discussed. Advances in the synthesis, physicochemical behavior, and electrochemical stability of NaAlCl 4 , as well as the structural and conductive properties of Na-β-alumina and Na-β″-alumina Na-ion conductor phases, are presented. Particular attention is given to strategies for enhancing interfacial contact and ionic conductivity, including capillary wick designs and surface coatings to improve wettability. The integration of aluminum as a positive-electrode material offers a safer, more recyclable, and cost-effective alternative, potentially addressing limitations of traditional Na-Ni and Na-S systems. This review highlights both recent progress and remaining technical challenges, setting the stage for future developments in scalable, high-performance Na-Al molten salt batteries.