Molecular Dynamics Simulation Investigation of Freezing Point Depression in NaClO 4 Electrolyte Solution by CaCl 2 .

The development of inorganic antifreeze electrolytes is of paramount importance for the application of sodium-ion batteries under low-temperature conditions. However, there is little reported about their molecular mechanism for lowering the freezing point of electrolytes. Therefore, this study explores the mechanism by which CaCl 2 lowers the freezing point of the NaClO 4 electrolyte. Hexagonal ice (ice I h ) was used as the ice seed, and CaCl 2 was selected as the antifreeze agent. The coexistence system of ice and solution was constructed to simulate the freezing process. It was found that there is ion rejection at the ice layer, with ions predominantly distributed in the solution. Over time, ions form an ion adsorption layer at the ice-solution interface. The radial distribution function (RDF) and spatial distribution function (SDF) of Na + , ClO 4 - , Ca 2+ , and Cl - revealed that ions form the first solvation shells with water molecules. The interaction energy between ions and water molecules is greater than that between ice nuclei and water. Therefore, ions are better able to maintain the stability of their solvation shells and inhibit the growth of ice I h through a mechanism of competition for water molecules. Furthermore, the dissolution free energy of Na + and Ca 2+ in the aqueous phase was studied. The results indicated that Ca 2+ has a stronger affinity for water molecules than Na + , making it more competitive in competing for water with ice I h . Therefore, CaCl 2 in NaClO 4 solution can reduce the freezing point. This work provides a molecular-level understanding of how CaCl 2 reduces the freezing point of NaClO 4 solution, which is beneficial for designing strategies for low-temperature electrolytes.