Development of safe, low-cost, grid-scale electrical energy storage remains a national priority, critical to agile, reliable energy distribution, transformative renewable energy integration, effective emergency response, and even successful national defense initiatives. Viable candidate energy storage systems must be able to reliably provide the high capacity and power needed to meet evolving electrical demands while remaining cost-effective and safe. With current large scale battery technologies challenged by high cost, limited cyclability, and potentially hazardous runaway reaction behaviors, there is a clear need to develop alternative battery technologies. Here, I will describe a new generation of intermediate temperature molten sodium-based batteries, enabled by the solid state electrolyte NaSICON (Na Super Ion CONductor). NaSICON provides exceptional low-to-intermediate temperature sodium ion conductivity, exhibits excellent chemical and mechanical stability, and can be produced in a range of form factors on an industrial scale. Integrating molten sodium anodes, NaSICON solid state electrolytes, and AlCl₃-based molten salt catholytes, we create high performance, all-inorganic battery constructs that operate below 200^oC and avoid hazards associated with runaway exothermic reactions, polymer separators, and organic electrolytes used in other batteries. I will describe the design and scalable performance (up to 250Wh) of several emerging intermediate temperature molten salt technologies including Na-NiCl₂ and Na-I₂. These promising, intermediate temperature technologies boast coulombic efficiencies near 100% and energy efficiencies >80% through months of stable electrochemical cycling. Moreover, accelerated rate calorimetry verifies the inherent safety of these molten salt chemistries, revealing neither the runaway exothermic reactions nor hazardous pressurized gas generation that plague other large-scale battery systems. The encouraging performance of these intermediate temperature molten salt battery systems promises new opportunities to meet the need for reliable, safe, and cost-effective solutions to growing national challenges in grid-scale electrical energy storage.

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.