A sodium liquid metal battery based on the multi-cationic electrolyte for grid energy storage

Sodium-based batteries are very promising for large-scale applications in near future, thanks to the great abundance and low cost of sodium. Herein, a high-performance liquid metal battery with a negative electrode of metallic sodium is developed. As the metallic sodium has a low melting point (∼ 98°C) and weak corrosion to ceramic seals, the sodium liquid metal batteries (Na-LMBs) offer the merits of low operating temperature, low cost, long lifespan and high safety. However, sodium metal has a high solubility in the electrolyte of single-cationic molten sodium halide mixtures such as NaF-NaCl-NaI due to a high melting point above 500°C, resulting in high self-discharge and low coulombic efficiency. In this work, a multi-cationic ternary molten chloride salt mixture LiCl-NaCl-KCl (59:5:36 mol %) with a melting point lower than 400°C was designed as the electrolyte, which effectively inhibits the dissolution of sodium in the electrolyte. Further, by adopting a dual-active Bi9Sb alloy positive electrode, the active material utilization was improved. At 100 mA cm−2, the battery ran stably over 700 cycles at 450°C with a coulombic efficiency of 97%, and active material utilization of about 80%. The battery also exhibited decent rate performance within the current densities of 100-1000 mA cm−2. The calculation based on a 1 MW/5 MWh demo energy storage plant indicates that the estimated Levelized Cost of Storage (LCOS) of the Na-LMB is lower than 0.029 $/kWh. These results demonstrate the Na-LMB as a promising technology for grid-scale energy storage applications.