Enabling Low-Cost Molten Sodium Batteries Through Engineered Catholyte-Separator Materials Chemistry

Cost-effective, safe, and reliable batteries are expected to be key components of the emerging electrical energy grid. We describe here a new class of low-temperature molten sodium-iodide batteries that employ a molten sodium anode, a solid-state NaSICON ceramic separator, and a low-cost molten salt catholyte. These unique batteries operate near 100°C, a dramatic reduction from the ~300°C operation of traditional molten sodium batteries, and they offer significantly higher voltages (&gt;3.1V) than many other scalable battery chemistries. Enabling this low-temperature operation, however, requires significant understanding and control over materials chemistry and critical interfaces. Here, we will specifically discuss recent discoveries involving chemical interactions at the interface between the NaSICON ceramic and the molten sodium-iodide/aluminum chloride salt catholyte. We will discuss the unexpected dependence of battery cycling performance on molten salt composition and connect the battery performance to specific electrochemical and materials properties of the separator and the salt. In particular, we identify specific impact of catholyte Lewis acidity on key chemical interactions at this critical interface. Understanding these fundamental interactions provides key insights and guidance that are central to designing high performance molten sodium batteries that operate with low-cost catholyte salts.<br/>Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & 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.