Research progress of molten salt electrolyte and separator materials for thermal batteries

As a reserve battery that heats the electrolyte to melt when applied to use, thermal batteries are mostly used in military and aerospace fields. At room temperature, its electrolyte is in a solid state without ionic conduction, so that the battery does not self-discharge, which is a necessary condition for its long-term storage. The molten salt electrolyte of the thermal battery is one of the key elements that determine its performance. In recent years, the application of a new system of component-controlled molten salt electrolyte to reduce the melting point and increase the ionic conductivity has become one of the research hotspots such as adding low-melting component salts to lower the melting point of the molten salt system, or using the entropy increase principle to optimize the performance of molten salt by adding new components. Combining with theoretical calculations and simulations, the ternary or even quaternary molten salt is developed to improve thermal battery performance, especially to extend battery life. In order to make the use of thermal batteries more common, the molten salt of the low melting point system is utilized. The introduction of some precious metal cations and the use of nitrates can reduce the melting temperature of the molten salt system to below 300℃, which is the standard for its common use. The addition of functional components such as MgO binder can reduce the probability of electrolyte molten salt leakage, but its dosage and structure need to be optimized to reduce the internal resistance of the battery and improve the retention of molten salt, which can improve the electrochemical performance of thermal batteries. Further, the introduction of inorganic fiber separators can reduce or eliminate the use of MgO binder to a greater extent and improve the safety and reliability of the battery, which also provides guidance for miniaturization of thermal battery. © 2021, Chemical Industry Press Co., Ltd. All right reserved.