Multi-cationic molten salt electrolyte of high-performance sodium liquid metal battery for grid storage

Multi-cationic molten chloride salt mixtures such as LiCl-KCl-NaCl are promising molten salt electrolytes for low-temperature (lower than 450°C) sodium liquid metal batteries (Na-LMBs). In this work, the melting temperature of LiCl-KCl-NaCl was determined with Differential Scanning Calorimetry (DSC), assisted by FactSageTM and confirmed by a melting point apparatus OptiMeltTM. It is founded that the eutectic LiCl-KCl-NaCl can be considered as a pseudo-binary system with LiCl-KCl eutectic (59.2-40.8 mol.%) as the solvent and NaCl as the solute. When NaCl is not more than 9 mol.%, the eutectic LiCl-KCl-NaCl salt mixture has a melting temperature of ~350°C as that of LiCl-KCl eutectic. In addition, the exchange reactions between anode Na metal with LiCl-KCl-NaCl molten salt electrolyte were studied at the temperature of 400-500 °C quantitatively. The equilibrium constants of the exchange reactions were determined by chemical analysis on the salt and metal phases with Ion Chromatography (IC). A one ampere-hour (Ah) Na-LMB test cell shows promising energy storage performance. Moreover, the phenomena in the cell test can be explained convincingly, combining the results of exchange reactions and the pseudo-binary-system theory. The findings on the multi-cationic molten salt electrolytes for Na-LMBs in this work could support further development of other liquid metal batteries