In situ displacement reactions of molten sodium anode and multi-cationic halide electrolytes enabling high-performance liquid metal batteries

Abstract

Sodium liquid metal battery has attracted attention for large-scale energy storage applications due to its low-cost, long-lifespan and high-safety. However, the self-discharging caused by sodium dissolving in the molten salt electrolyte reduces the efficiency of the battery and restricts the practical development of this chemistry. In this work, a low-melting point multi-cationic electrolyte (LiCl-NaCl-KCl) was designed to inhibit the dissolution of sodium in the electrolyte. The displacement reaction of Na and molten LiCl at high temperature were revealed for the first time, and the mechanism of improving battery performance was demonstrated in the Na| LiCl-NaCl-KCl |Sb-Bi batteries. Based on the displacement reaction mechanisms, the Na||Bi9Sb cell based on LiCl-KCl (54:46 mol%) electrolyte, without NaCl at the initial state, was constructed, which exhibited high coulombic efficiency of over 98 % and excellent cyclic performance (∼100 % capacity retention after 2500 cycles) at 450 °C. This work provides a unique idea of electrolyte design that can both inhibit the dissolution of metals in molten salts and ensure long-term stable battery operation by using electrolyte–electrode interactions, and provides a new way for the practical development of low-cost and long-lifespan liquid metal battery energy storage technology.