Résumé
Molten salt electrolytes play a crucial role in thermal battery cells, offering excellent electrochemical performance and zero self-discharge at room temperature before melting. However, the transport properties of ionic species in these media are not well understood, and much remains unknown about the factors that determine the effectiveness of one electrolyte over another.
This study investigates the mobility of ionic species, particularly lithium and fluorine, in eutectic molten salt mixtures like LiF-LiCl-LiBr, commonly used in thermal batteries. Using advanced in situ high-temperature techniques, including high-temperature nuclear magnetic resonance (HT-NMR), pulsed field gradients (PFG), and electrochemical impedance spectroscopy (EIS), we aim to understand the ionic motion processes. The research also examines the binding of these salts with an MgO powder and the effect of compaction on retention properties.
The LiF-LiCl-LiBr eutectic shows superior ionic conductivity compared to systems like LiCl-KCl due to its higher lithium concentration and greater lithium mobility. Lithium diffuses faster than other ionic species, such as fluorine, but its high melting point of 440 • C limits its operational temperature range. The compaction rate of bound pellets is key to electrolyte performance, influencing ionic mobility. Higher compaction enhances lithium diffusion but may cause leakage above certain thresholds, depending on salt type and temperature.
This innovative approach enables rapid testing of various electrolytic compositions and binders, helping assess performance and the impact of manufacturing processes.