As the national electrical energy grid continues to expand and evolve, there is an increasing need for safe, cost-effective and reliable large scale batteries. Current large scale battery technologies continue to suffer from limited cyclability, high cost, and potentially hazardous runaway reaction behaviors. Here, we describe a promising alternative approach to intermediate temperature molten sodium-based batteries, enabled by advanced solid state ceramic electrolytes, such as NaSICON, that offer high Na⁺ conductivity at temperatures well below 200 °C. Integrating molten sodium anodes, ceramic solid state electrolytes, and fully molten AlCl₃-based molten salt catholytes, we create high performance, all-inorganic batteries. In particular, we explore an AlCl₃-NaI molten salt catholyte, and we show that these batteries operate efficiently below 200 °C. We describe the relationships between the molten salt composition and electrochemical properties of the catholyte, revealing how these promising, intermediate temperature technologies boast coulombic efficiencies near 100% and energy efficiencies >80%. Moreover, we validate the safety of this material set using accelerated rate calorimetry to demonstrate that the system exhibits neither the runaway exothermic reactions nor hazardous pressurized gas generation that plague other large-scale battery systems. Finally, we discuss the potential benefits to long term battery reliability afforded by low-to-intermediate temperature battery operation. The encouraging performance of this emergent intermediate temperature molten salt battery shows a path to providing the reliable, safe, and cost-effective energy storage solutions demanded by our rapidly growing national electrical energy grid.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.