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 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 FactSage™ simulation and confirmed by a melting point apparatus OptiMelt™. 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.